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diff --git a/libs/optional/doc/html/boost_optional/reference/detailed_semantics.html b/libs/optional/doc/html/boost_optional/reference/detailed_semantics.html deleted file mode 100644 index dfbfc871f..000000000 --- a/libs/optional/doc/html/boost_optional/reference/detailed_semantics.html +++ /dev/null @@ -1,2098 +0,0 @@ -<html> -<head> -<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> -<title>Detailed Semantics</title> -<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> -<meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> -<link rel="home" href="../../index.html" title="Boost.Optional"> -<link rel="up" href="../../optional/reference.html" title="Reference"> -<link rel="prev" href="../../optional/reference.html" title="Reference"> -<link rel="next" href="../dependencies_and_portability.html" title="Dependencies and Portability"> -</head> -<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> -<table cellpadding="2" width="100%"><tr> -<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> -<td align="center"><a href="../../../../../../index.html">Home</a></td> -<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> -<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> -<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> -<td align="center"><a href="../../../../../../more/index.htm">More</a></td> -</tr></table> -<hr> -<div class="spirit-nav"> -<a accesskey="p" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> -</div> -<div class="section"> -<div class="titlepage"><div><div><h3 class="title"> -<a name="boost_optional.reference.detailed_semantics"></a><a class="link" href="detailed_semantics.html" title="Detailed Semantics">Detailed - Semantics</a> -</h3></div></div></div> -<p> - Because <code class="computeroutput"><span class="identifier">T</span></code> might be of reference - type, in the sequel, those entries whose semantic depends on <code class="computeroutput"><span class="identifier">T</span></code> being of reference type or not will be - distinguished using the following convention: - </p> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code><span class="emphasis"><em>(not - a ref)</em></span><code class="computeroutput"><span class="special">></span></code>, the - description corresponds only to the case where <code class="computeroutput"><span class="identifier">T</span></code> - is not of reference type. - </li> -<li class="listitem"> - If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>, the description corresponds - only to the case where <code class="computeroutput"><span class="identifier">T</span></code> - is of reference type. - </li> -<li class="listitem"> - If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>, the description is the same for - both cases. - </li> -</ul></div> -<div class="note"><table border="0" summary="Note"> -<tr> -<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> -<th align="left">Note</th> -</tr> -<tr><td align="left" valign="top"><p> - The following section contains various <code class="computeroutput"><span class="identifier">assert</span><span class="special">()</span></code> which are used only to show the postconditions - as sample code. It is not implied that the type <code class="computeroutput"><span class="identifier">T</span></code> - must support each particular expression but that if the expression is supported, - the implied condition holds. - </p></td></tr> -</table></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<h5> -<a name="boost_optional.reference.detailed_semantics.h0"></a> - <span class="phrase"><a name="boost_optional.reference.detailed_semantics.optional_class_member_functions"></a></span><a class="link" href="detailed_semantics.html#boost_optional.reference.detailed_semantics.optional_class_member_functions">optional - class member functions</a> - </h5> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span> - <span class="keyword">noexcept</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Default-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> T's default constructor <span class="underline">is not</span> called. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>'s - default constructor <span class="underline">is not</span> called. - The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code> - denotes an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code> - that can be used as the parameter. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">none</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">n</span><span class="special">(</span><span class="identifier">none</span><span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">n</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> - is <code class="computeroutput"><span class="keyword">true</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> - and its value is a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">v</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> is called. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">);</span></code> - in that case, this constructor has no effect. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">)</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> - and its value is an instance of an internal type wrapping the reference - <code class="computeroutput"><span class="identifier">ref</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> -<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span> -<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor_move_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> - <span class="identifier">v</span> <span class="special">)</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> - is <code class="computeroutput"><span class="keyword">true</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Directly-Move-Constructs an - <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> - and its value is move-constructed from <code class="computeroutput"><span class="identifier">v</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> - throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> - is called. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> - <span class="special">);</span></code> in that case, the state of - <code class="computeroutput"><span class="identifier">v</span></code> is determined by exception - safety guarantees for <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v1</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v1</span><span class="special">));</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v2</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> - <span class="identifier">ref</span> <span class="special">)</span> - <span class="special">=</span> <span class="keyword">delete</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> This constructor is deleted - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> - <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> - <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> - <span class="identifier">T</span><span class="special">&</span> - <span class="identifier">v</span> <span class="special">)</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - If condition is true, same as: - </li></ul></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> - <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> - <span class="identifier">v</span> <span class="special">)</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - otherwise, same as: - </li></ul></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> - <span class="special">::</span><span class="identifier">optional</span><span class="special">()</span></code> - </p></blockquote></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">rhs</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> - is <code class="computeroutput"><span class="keyword">true</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If rhs is initialized, - <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the value - of <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If rhs is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> - is called. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">);</span></code> - in that case, this constructor has no effect. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uninit</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is another reference to the same object - referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; - else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> - will refer to the same object (they alias). - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uninit</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> - -<span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_move_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> - <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code> - is <code class="computeroutput"><span class="keyword">true</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is move constructed from <code class="computeroutput"><span class="identifier">rhs</span></code>; - else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> - throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="special">&&</span> - <span class="special">)</span></code> is called. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> - <span class="special">);</span></code> in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains initialized and the value - of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> - is determined by exception safety of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uninit</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="keyword">nullptr</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span> <span class="special">&&</span> - <span class="identifier">rhs</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Move-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is another reference to the same object - referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; - else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> - will refer to the same object (they alias). - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uninit</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span> - -<span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> - -<span class="special">*</span><span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the value - of rhs converted to type <code class="computeroutput"><span class="identifier">T</span></code>; - else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> is called if <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code> to <code class="computeroutput"><span class="identifier">T</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">);</span></code> - in that case, this constructor has no effect. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_move_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> - <span class="identifier">rhs</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is move-constructed from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code> - throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code> - is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, - which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code> - to <code class="computeroutput"><span class="identifier">T</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> - <span class="special">);</span></code> in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains initialized and the value - of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> - is determined by exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">))</span> <span class="special">;</span> -<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_constructor_factory"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span> - <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span> - <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained from the factory. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> - and its value is <span class="emphasis"><em>directly given</em></span> from the factory - <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value <span class="underline">is not copied</span>). - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> - constructor called by the factory throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../tutorial/in_place_factories.html" title="In-Place Factories">In-Place - Factories</a> - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code> - constructor used by the factory; in that case, this constructor has no - effect. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">C</span> <span class="special">{</span> <span class="identifier">C</span> <span class="special">(</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span> - -<span class="identifier">C</span> <span class="identifier">v</span><span class="special">(</span><span class="char">'A'</span><span class="special">,</span><span class="number">123.4</span><span class="special">,</span><span class="string">"hello"</span><span class="special">);</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">in_place</span> <span class="special">(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// InPlaceFactory used</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">in_place</span><span class="special"><</span><span class="identifier">C</span><span class="special">>(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// TypedInPlaceFactory used</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_equal_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized destroys its contained - value. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">rhs</span> <span class="special">)</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Assigns the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is a - <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">rhs</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code> - throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s - assignment operator is used, otherwise, its copy-constructor is used. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> In the event of an - exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified - as far as <code class="computeroutput"><span class="identifier">optional</span></code> is - concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s - <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>). - If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s - <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span> - -<span class="identifier">T</span> <span class="identifier">y</span><span class="special">;</span> -<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> - <span class="identifier">rhs</span> <span class="special">)</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> (Re)binds the wrapped reference. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references - the same object referenced by <code class="computeroutput"><span class="identifier">rhs</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, it is <span class="emphasis"><em>rebound</em></span> - to the new object. See <a class="link" href="../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a> - for details on this behavior. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span> -<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> -<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> -<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span> - -<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span> -<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span> -<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span> -<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span> -<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span> -<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_move_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span> - <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Moves the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is moved - from <code class="computeroutput"><span class="identifier">rhs</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> - or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&&)</span></code> - throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s - move-assignment operator is used, otherwise, its move-constructor is - used. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> In the event of an - exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified - as far as <code class="computeroutput"><span class="identifier">optional</span></code> is - concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s - <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>). - If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s - <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span> - -<span class="identifier">T</span> <span class="identifier">y1</span><span class="special">,</span> <span class="identifier">y2</span><span class="special">,</span> <span class="identifier">yR</span><span class="special">;</span> -<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y1</span><span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y2</span><span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> - <span class="identifier">rhs</span> <span class="special">)</span> - <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> This assignment operator is deleted. - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">rhs</span> <span class="special">)</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> - is <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">CopyAssignable</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> - <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> -<li class="listitem"> - If <code class="computeroutput"><span class="special">!*</span><span class="keyword">this</span> - <span class="special">&&</span> <span class="special">!</span><span class="identifier">rhs</span></code> no effect, otherwise - </li> -<li class="listitem"> - if <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> - <span class="special">&&</span> <span class="special">!</span><span class="identifier">rhs</span></code>, destroys the contained value - by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, otherwise - </li> -<li class="listitem"> - if <code class="computeroutput"><span class="special">!*</span><span class="keyword">this</span> - <span class="special">&&</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>, initializes the contained value - as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> - with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>, - otherwise - </li> -<li class="listitem"> - (if <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> - <span class="special">&&</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>) assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> to the contained value. - </li> -</ul></div> - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>; - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> If any exception is - thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code> - remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s copy constructor, no effect. If - an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s - copy assignment, the state of its contained value is as defined by the - exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s - copy assignment. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> - -<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span> -<span class="comment">// previous value (copy of 'v') destroyed from within 'opt'.</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> - <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> (Re)binds thee wrapped reference. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references - the same object referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; otherwise, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized (and references - no object). - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized and so is <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>, - <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is <span class="emphasis"><em>rebound</em></span> to the new object. See <a class="link" href="../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a> - for details on this behavior. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span> -<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> -<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> -<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span> - -<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span> -<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span> -<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span> -<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span> -<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span> -<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_move_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> - <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> - is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> - and <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> - <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> -<li class="listitem"> - If <code class="computeroutput"><span class="special">!*</span><span class="keyword">this</span> - <span class="special">&&</span> <span class="special">!</span><span class="identifier">rhs</span></code> no effect, otherwise - </li> -<li class="listitem"> - if <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> - <span class="special">&&</span> <span class="special">!</span><span class="identifier">rhs</span></code>, destroys the contained value - by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, otherwise - </li> -<li class="listitem"> - if <code class="computeroutput"><span class="special">!*</span><span class="keyword">this</span> - <span class="special">&&</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>, initializes the contained value - as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> - with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, - otherwise - </li> -<li class="listitem"> - (if <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> - <span class="special">&&</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>) assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value. - </li> -</ul></div> - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>; - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span> <span class="special">&&</span> - <span class="identifier">is_nothrow_move_assignable</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> If any exception is - thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code> - remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s move constructor, the state of - <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> - is determined by the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s - move constructor. If an exception is thrown during the call to T's move-assignment, - the state of <code class="computeroutput"><span class="special">**</span><span class="keyword">this</span></code> - and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> - is determined by the exception safety guarantee of T's move assignment. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> - -<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> - <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&&</span> <span class="identifier">rhs</span> - <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Same as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> - <span class="special">)</span></code>. - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Assigns another convertible - optional to an optional. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the value - of <code class="computeroutput"><span class="identifier">rhs</span></code> <span class="emphasis"><em>converted</em></span> - to type <code class="computeroutput"><span class="identifier">T</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and rhs are initially initialized, - <code class="computeroutput"><span class="identifier">T</span></code>'s <span class="emphasis"><em>assignment - operator</em></span> (from <code class="computeroutput"><span class="identifier">U</span></code>) - is used. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initially initialized but <code class="computeroutput"><span class="identifier">rhs</span></code> - is uninitialized, <code class="computeroutput"><span class="identifier">T</span></code>'s - <span class="emphasis"><em>destructor</em></span> is called. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initially uninitialized but rhs - is initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s - <span class="emphasis"><em>converting constructor</em></span> (from <code class="computeroutput"><span class="identifier">U</span></code>) - is called. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> In the event of an - exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified - as far as optional is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s - <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>). - If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s - converting constructor fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span> - -<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt0</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_move_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span> - <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Move-assigns another convertible - optional to an optional. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code> - is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initialized and its value is moved from the value of <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code> - or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> - <span class="special">)</span></code> throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> If both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code> - are initially initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s - <span class="emphasis"><em>assignment operator</em></span> (from <code class="computeroutput"><span class="identifier">U</span><span class="special">&&</span></code>) is used. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initially initialized but <code class="computeroutput"><span class="identifier">rhs</span></code> - is uninitialized, <code class="computeroutput"><span class="identifier">T</span></code>'s - <span class="emphasis"><em>destructor</em></span> is called. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initially uninitialized but <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s - <span class="emphasis"><em>converting constructor</em></span> (from <code class="computeroutput"><span class="identifier">U</span><span class="special">&&</span></code>) is called. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> In the event of an - exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified - as far as optional is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s - <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>). - If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s - converting constructor fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span> - -<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt1</span> <span class="special">)</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_emplace"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">emplace</span><span class="special">(</span> <span class="identifier">Args</span><span class="special">...&&</span> - <span class="identifier">args</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> The compiler supports rvalue - references and variadic templates. - </li> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized calls <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code>. - Then initializes in-place the contained value as if direct-initializing - an object of type <code class="computeroutput"><span class="identifier">T</span></code> with - <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever the selected <code class="computeroutput"><span class="identifier">T</span></code>'s constructor throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> - need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> - or <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>. On - compilers that do not support variadic templates, the signature falls - back to single-argument: <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">)</span></code>. On compilers that do not support rvalue - references, the signature falls back to two overloads: taking <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code> - lvalue reference. - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> If an exception is - thrown during the initialization of <code class="computeroutput"><span class="identifier">T</span></code>, - <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - is <span class="emphasis"><em>uninitialized</em></span>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">;</span> -<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> <span class="comment">// create in-place using ctor T(int)</span> -<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">();</span> <span class="comment">// destroy previous and default-construct another T</span> -<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// destroy and copy-construct in-place (no assignment called)</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_equal_factory"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">InPlaceFactory</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">f</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">TypedInPlaceFactory</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">f</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effect:</strong></span> Assigns an <code class="computeroutput"><span class="identifier">optional</span></code> - with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained - from the factory. - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span> - and its value is <span class="emphasis"><em>directly given</em></span> from the factory - <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value <span class="underline">is not copied</span>). - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> - constructor called by the factory throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../tutorial/in_place_factories.html" title="In-Place Factories">In-Place - Factories</a> - </li> -<li class="listitem"> - <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only - be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code> - constructor used by the factory; in that case, the <code class="computeroutput"><span class="identifier">optional</span></code> - object will be reset to be <span class="emphasis"><em>uninitialized</em></span>. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Deprecated:</strong></span> same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">v</span><span class="special">)</span> - <span class="special">;</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_reset"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">none_t</span> - <span class="special">);</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_get"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">get</span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> - <span class="special">&)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> A reference to the contained - value - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via - <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">get</span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> - <span class="keyword">const</span><span class="special">&</span> - <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">&)</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span> - reference contained. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via - <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_asterisk"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> A reference to the contained - value - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via - <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. - On compilers that do not support ref-qualifiers on member functions these - two overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> - and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span> -<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">T</span> <span class="identifier">w</span> <span class="special">;</span> -<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">w</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">w</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_asterisk_move"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value. - </li> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">);</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via - <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. - On compilers that do not support ref-qualifiers on member functions this - overload is not present. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span> - reference contained. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via - <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. - On compilers that do not support ref-qualifiers on member functions these - three overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code> - member functions. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span> -<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span> -<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> On compilers that do not support - ref-qualifiers on member functions these two overloads are replaced with - the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> - and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">,</span> <span class="identifier">o1</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">);</span> - -<span class="keyword">try</span> <span class="special">{</span> - <span class="identifier">o0</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// throws</span> - <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">false</span> <span class="special">);</span> -<span class="special">}</span> -<span class="keyword">catch</span><span class="special">(</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span> - <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">true</span> <span class="special">);</span> -<span class="special">}</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_value_move"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">throw</span> - <span class="identifier">bad_optional_access</span><span class="special">();</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> On compilers that do not support - ref-qualifiers on member functions this overload is not present. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span> - <span class="identifier">v</span><span class="special">)</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> - <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code> - is not <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code> - is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>, - the program is ill-formed. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> On compilers that do not support - ref-qualifiers on member functions this overload is replaced with the - <code class="computeroutput"><span class="keyword">const</span></code>-qualified member function. - On compilers without rvalue reference support the type of <code class="computeroutput"><span class="identifier">v</span></code> becomes <code class="computeroutput"><span class="identifier">U</span> - <span class="keyword">const</span><span class="special">&</span></code>. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_value_or_move"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span> - <span class="identifier">v</span><span class="special">)</span> - <span class="special">&&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code> - is not <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> - or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code> - is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>, - the program is ill-formed. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> On compilers that do not support - ref-qualifiers on member functions this overload is not present. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_value_or_call"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> - is <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> whose result type - is convertible to <code class="computeroutput"><span class="identifier">T</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span> - <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">();</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> On compilers that do not support - ref-qualifiers on member functions this overload is replaced with the - <code class="computeroutput"><span class="keyword">const</span></code>-qualified member function. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">complain_and_0</span><span class="special">()</span> -<span class="special">{</span> - <span class="identifier">clog</span> <span class="special"><<</span> <span class="string">"no value returned, using default"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> - <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> -<span class="special">}</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">none</span><span class="special">;</span> - -<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun not called</span> -<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span> - -<span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">oN</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun called</span> -<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_value_or_call_move"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> - is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> - and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> - whose result type is convertible to <code class="computeroutput"><span class="identifier">T</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span> - <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> - <span class="identifier">f</span><span class="special">();</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> On compilers that do not support - ref-qualifiers on member functions this overload is not present. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> - <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> - <span class="keyword">default</span> <span class="special">)</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> - <span class="keyword">const</span><span class="special">&</span> - <span class="identifier">get_optional_value_or</span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get_optional_value_or</span> - <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>&</span> - <span class="identifier">o</span><span class="special">,</span> - <span class="identifier">T</span><span class="special">&</span> - <span class="keyword">default</span> <span class="special">)</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Deprecated:</strong></span> Use <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code> instead. - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> A reference to the contained - value, if any, or <code class="computeroutput"><span class="keyword">default</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">,</span> <span class="identifier">z</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span><span class="special">;</span> -<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">def</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">y</span> <span class="special">==</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span> -<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">get_optional_value_or</span><span class="special">(</span><span class="identifier">opt</span><span class="special">,</span><span class="identifier">z</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">!=</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span> - <span class="keyword">const</span><span class="special">*</span> - <span class="identifier">get_pointer</span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span> - <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> - <span class="special">&)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized, a pointer to the - contained value; else <code class="computeroutput"><span class="number">0</span></code> (<span class="emphasis"><em>null</em></span>). - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> The contained value is permanently - stored within <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>, - so you should not hold nor delete this pointer - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">copt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> -<span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span> -<span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">cp</span> <span class="special">=</span> <span class="identifier">copt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">();</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">p</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">opt</span><span class="special">)</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">cp</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">copt</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> - <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span> - <span class="keyword">const</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> - <span class="special">->()</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized. - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> A pointer to the contained - value. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> Nothing. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via - <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> <span class="keyword">int</span> <span class="identifier">mdata</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span> -<span class="identifier">X</span> <span class="identifier">x</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span> -<span class="identifier">opt</span><span class="special">-></span><span class="identifier">mdata</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span> - <span class="keyword">bool</span><span class="special">()</span> - <span class="keyword">const</span> <span class="keyword">noexcept</span> - <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> On compilers that do not support - explicit conversion operators this falls back to safe-bool idiom. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">==</span> <span class="number">0</span> <span class="special">);</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">);</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">noexcept</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>; - else <code class="computeroutput"><span class="keyword">false</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> This operator is provided for - those compilers which can't use the <span class="emphasis"><em>unspecified-bool-type operator</em></span> - in certain boolean contexts. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">opt</span> <span class="special">);</span> -<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">some_T</span> <span class="special">;</span> - -<span class="comment">// Notice the "double-bang" idiom here.</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!!</span><span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_optional_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">explicit</span> - <span class="keyword">operator</span> <span class="keyword">bool</span> - <span class="special">()</span> <span class="special">;</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<h5> -<a name="boost_optional.reference.detailed_semantics.h1"></a> - <span class="phrase"><a name="boost_optional.reference.detailed_semantics.free_functions"></a></span><a class="link" href="detailed_semantics.html#boost_optional.reference.detailed_semantics.free_functions">Free - functions</a> - </h5> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span> - type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> - -<span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional<int></span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> - <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">condition</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span> - type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">calculate_foo</span><span class="special">()</span> -<span class="special">{</span> - <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span> - <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span> -<span class="special">}</span> - -<span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span> -<span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span> - <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> - shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>. - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code> - and <code class="computeroutput"><span class="identifier">y</span></code> are initialized, - <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span> - <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>. - If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>. - If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> Pointers have shallow relational - operators while <code class="computeroutput"><span class="identifier">optional</span></code> - has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect - to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a> - instead - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span> <span class="comment">// Identity implies equality</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">//</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">// Initialized unequal to initialized.</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span> <span class="comment">//</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special"><</span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span></code> - shall be well-formed and its result shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> - <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> Pointers have shallow relational - operators while <code class="computeroutput"><span class="identifier">optional</span></code> - has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> directly in generic code which expect - to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a> - instead. <code class="computeroutput"><span class="identifier">T</span></code> need not be - <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only single - <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> - is required. Other relational operations are defined in terms of this - one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> - satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity, - antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optinal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Identity implies equivalence</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">o0</span> <span class="special">);</span> <span class="comment">// Uninitialized is less than initialized</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> - -<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Two initialized compare as (*lhs < *rhs)</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> -</pre> - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> - <span class="identifier">x</span> <span class="special">==</span> - <span class="identifier">y</span> <span class="special">);</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">></span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span> - <span class="identifier">y</span> <span class="special"><</span> - <span class="identifier">x</span> <span class="special">);</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special"><=</span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> - <span class="identifier">y</span> <span class="special"><</span> - <span class="identifier">x</span> <span class="special">);</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">>=</span> <span class="special">(</span> - <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> - <span class="identifier">x</span> <span class="special"><</span> - <span class="identifier">y</span> <span class="special">);</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> - <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">==</span> <span class="special">(</span> <span class="identifier">none_t</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code> - need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>. - </li> -</ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> - <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span> - <span class="special">!=</span> <span class="special">(</span> <span class="identifier">none_t</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> - <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span> - <span class="identifier">x</span> <span class="special">==</span> - <span class="identifier">y</span> <span class="special">);</span></code> - </li></ul></div> -<p> - <span class="inlinemediaobject"><img src="../../images/space.png" alt="space"></span> - </p> -<a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p> - <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span> - <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">y</span> - <span class="special">)</span> <span class="special">;</span></code> - </p></blockquote></div> -<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> -<li class="listitem"> - <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>. - </li> -<li class="listitem"> - <span class="bold"><strong>Effects:</strong></span> - <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> -<li class="listitem"> - If <code class="computeroutput"><span class="special">!*</span><span class="keyword">this</span> - <span class="special">&&</span> <span class="special">!</span><span class="identifier">rhs</span></code>, no effect, otherwise - </li> -<li class="listitem"> - if <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> - <span class="special">&&</span> <span class="special">!</span><span class="identifier">rhs</span></code>, initializes the contained - value of <code class="computeroutput"><span class="identifier">rhs</span></code> as - if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> - with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">))</span></code>, followed by <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value and - <code class="computeroutput"><span class="identifier">rhs</span></code> contains a - value, otherwise - </li> -<li class="listitem"> - if <code class="computeroutput"><span class="special">!*</span><span class="keyword">this</span> - <span class="special">&&</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>, initializes the contained value - of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> - as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> - with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code> does not contain a value, - otherwise - </li> -<li class="listitem"> - (if <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> - <span class="special">&&</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>) calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code>. - </li> -</ul></div> - </li> -<li class="listitem"> - <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code> - interchanged. - </li> -<li class="listitem"> - <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever - <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code> - throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code> - throws. - </li> -<li class="listitem"> - <span class="bold"><strong>Example:</strong></span> -<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span> -<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span> -<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span> - -<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span> - -<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span> - -<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span> - -<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span> -<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span> -</pre> - </li> -</ul></div> -</div> -<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> -<td align="left"></td> -<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p> - Distributed under the Boost Software License, Version 1.0. (See accompanying - file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) - </p> -</div></td> -</tr></table> -<hr> -<div class="spirit-nav"> -<a accesskey="p" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> -</div> -</body> -</html> |