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Boost Library Requirements and Guidelines
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<h1 align="left">
Boost Library Requirements and Guidelines
</h1>
<p align="left">
<a href="#Introduction">Introduction</a><br>
<a href="#Requirements">Requirements</a><br>
<a href="#License">License requirements</a><br>
<a href="#Portability">Portability requirements</a><br>
<a href="#Ownership">Ownership</a><br>
<a href="#Guidelines">Guidelines</a><br>
<a href="#Design_and_Programming">Design and
programming</a><br>
<a href="#Directory_structure">Directory structure and
filenames</a><br>
<a href="#Naming_consistency">Naming
consistency</a><br>
<a href="#Documentation">Documentation</a><br>
<a href="#Rationale">Rationale</a><br>
<a href=
"#Exception-specification">Exception-specification rationale</a><br>
<a href="#Naming">Naming conventions rationale</a><br>
<a href="#code_fonts">Source code fonts
rationale</a><br>
<a href="#Tabs">Tabs rationale</a><br>
<a href="#JavaScript">ECMAScript/JavaScript
rationale</a><br>
<a href="#Rationale_rationale">Rationale
rationale</a><br>
<a href="#Acknowledgements">Acknowledgements
rationale</a>
</p>
<h2 align="left">
<a name="Introduction" id="Introduction">Introduction</a>
</h2>
<p align="left">
This page describes requirements and guidelines for the content of a
library submitted to Boost.
</p>
<p align="left">
See the <a href="submission_process.htm">Boost Library Submission
Process</a> page for a description of the process involved.
</p>
<h2 align="left">
<a name="Requirements" id="Requirements">Requirements</a>
</h2>
<p>
To avoid the frustration and wasted time of a proposed library being
rejected, it must meets these requirements:
</p>
<ul>
<li>The license must meet the <a href="#License">license requirements</a>
below. Restricted licenses like the GPL and LGPL are not acceptable.
</li>
<li>The copyright <a href="#Ownership">ownership</a> must be clear.
</li>
<li>The library must be generally useful and not restricted to a narrow
problem domain.
</li>
<li>The library must meet the <a href="#Portability">portability
requirements</a> below.
</li>
<li>The library must come reasonably close to meeting the <a href=
"#Guidelines">Guidelines</a> below.
<ul>
<li>
<a href="#Design_and_Programming">Design and Programming</a>
</li>
<li>
<a href="#Directory_structure">Directory Structure</a>
</li>
<li>
<a href="#Documentation">Documentation</a>
</li>
</ul>
</li>
<li>The author must be willing to participate in discussions on the mailing
list, and to refine the library accordingly.
</li>
</ul>
<p>
There's no requirement that an author read the mailing list for a time
before making a submission. It has been noted, however, that submissions
which begin "I just started to read this mailing list ..." seem to fail,
often embarrassingly.
</p>
<h3 align="left">
<a name="License" id="License">License</a> requirements
</h3>
<p>
The preferred way to meet the license requirements is to use the <a href=
"../LICENSE_1_0.txt">Boost Software License</a>. See <a href=
"license_info.html">license information</a>. If for any reason you do not
intend to use the Boost Software License, please discuss the issues on the
Boost <a href="mailing_lists.htm#main">developers mailing list</a> first.
</p>
<p>
The license requirements:
</p>
<ul>
<li>Must be simple to read and understand.
</li>
<li>Must grant permission without fee to copy, use and modify the software
for any use (commercial and non-commercial).
</li>
<li>Must require that the license appear on all copies of the software
source code.
</li>
<li>Must not require that the license appear with executables or other
binary uses of the library.
</li>
<li>Must not require that the source code be available for execution or
other binary uses of the library.
</li>
<li>May restrict the use of the name and description of the library to the
standard version found on the Boost web site.
</li>
</ul>
<h3 align="left">
<a name="Portability" id="Portability">Portability</a> requirements
</h3>
<ul>
<li>
<p align="left">
A library's interface must portable and not restricted to a particular
compiler or operating system.
</p>
</li>
<li>
<p align="left">
A library's implementation must if possible be portable and not
restricted to a particular compiler or operating system. If a
portable implementation is not possible, non-portable constructions are
acceptable if reasonably easy to port to other environments, and
implementations are provided for at least two popular operating systems
(such as UNIX and Windows).
</p>
</li>
<li>
<p align="left">
There is no requirement that a library run on C++ compilers which do
not conform to the ISO standard.
</p>
</li>
<li>
<p align="left">
There is no requirement that a library run on any particular C++
compiler. Boost contributors often try to ensure their libraries
work with popular compilers. The boost/config.hpp <a href=
"../libs/config/config.htm">configuration header</a> is the preferred
mechanism for working around compiler deficiencies.
</p>
</li>
</ul>
<p align="left">
Since there is no absolute way to prove portability, many boost submissions
demonstrate practical portability by compiling and executing correctly with
two different C++ compilers, often under different operating systems.
Otherwise reviewers may disbelieve that porting is in fact practical.
</p>
<h3 align="left">
<a name="Ownership" id="Ownership">Ownership</a>
</h3>
<p align="left">
Are you sure you own the library you are thinking of
submitting? "How to Copyright Software" by MJ Salone, Nolo
Press, 1990 says:
</p>
<blockquote>
<p align="left">
Doing work on your own time that is very similar to programming you do
for your employer on company time can raise nasty legal problems.
In this situation, it's best to get a written release from your employer
in advance.
</p>
</blockquote>
<p align="left">
Place a copyright notice in all the important files you submit. Boost won't
accept libraries without clear copyright information.
</p>
<h2 align="left">
<a name="Guidelines" id="Guidelines">Guidelines</a>
</h2>
<p align="left">
Please use these guidelines as a checklist for preparing the content a
library submission. Not every guideline applies to every library, but
a reasonable effort to comply is expected.
</p>
<h3>
<a name="Design_and_Programming" id="Design_and_Programming">Design and
Programming</a>
</h3>
<ul>
<li>Aim first for clarity and correctness; optimization should be only a
secondary concern in most Boost libraries.
</li>
</ul>
<ul>
<li>Aim for ISO Standard C++. Than means making effective use of the
standard features of the language, and avoiding non-standard compiler
extensions. It also means using the C++ Standard Library where applicable.
</li>
</ul>
<ul>
<li>Headers should be good neighbors. See the <a href="header.htm">header
policy</a>. See <a href="#Naming_consistency">Naming consistency</a>.
</li>
</ul>
<ul>
<li>Follow quality programming practices. See, for example, "Effective C++"
2nd Edition, and "More Effective C++", both by Scott Meyers, published by
Addison Wesley.
</li>
</ul>
<ul>
<li>Use the C++ Standard Library or other Boost libraries, but only when
the benefits outweigh the costs. Do not use libraries other than the
C++ Standard Library or Boost. See <a href="library_reuse.htm">Library
reuse</a>.
</li>
</ul>
<ul>
<li>Read <a href="imp_vars.htm">Implementation Variation</a> to see how to
supply performance, platform, or other implementation variations.
</li>
</ul>
<ul>
<li>Read the <a href="separate_compilation.html">guidelines for libraries
with separate source</a> to see how to ensure that compiled link libraries
meet user expectations.
</li>
</ul>
<ul>
<li>Use the naming conventions of the C++ Standard Library (See <a href=
"#Naming">Naming conventions rationale</a>):<br>
<ul>
<li>Names (except as noted below) should be all lowercase, with words
separated by underscores.
</li>
<li>Acronyms should be treated as ordinary names (e.g.
<code>xml_parser</code> instead of <code>XML_parser</code>).
</li>
<li>Template parameter names begin with an uppercase letter.
</li>
<li>Macro (gasp!) names all uppercase and begin with BOOST_.
</li>
</ul>
</li>
</ul>
<ul>
<li>Choose meaningful names - explicit is better than implicit, and
readability counts. There is a strong preference for clear and descriptive
names, even if lengthy.
</li>
</ul>
<ul>
<li>Use exceptions to report errors where appropriate, and write code that
is safe in the face of exceptions.
</li>
</ul>
<ul>
<li>Avoid exception-specifications. See <a href="#Exception-specification">
exception-specification rationale</a>.
</li>
</ul>
<ul>
<li>Provide sample programs or confidence tests so potential users can see
how to use your library.
</li>
</ul>
<ul>
<li>Provide a regression test program or programs which follow the
<a href="test_policy.htm">Test Policies and Protocols</a>.
</li>
</ul>
<ul>
<li>Although some boost members use proportional fonts, tabs, and
unrestricted line lengths in their own code, boost's widely distributed
source code should follow more conservative guidelines:
<ul>
<li>Use fixed-width fonts. See <a href="#code_fonts">fonts
rationale</a>.
</li>
<li>Use spaces rather than tabs. See <a href="#Tabs">tabs
rationale</a>.
</li>
<li>Limit line lengths to 80 characters.
</li>
</ul>
</li>
</ul>
<ul>
<li>End all documentation files (HTML or otherwise) with a copyright
message and a licensing message. See <a href="license_info.html">license
information</a> page for the preferred form.
</li>
</ul>
<ul>
<li>Begin all source files (including programs, headers, scripts, etc.)
with:<br>
<ul>
<li>A comment line describing the contents of the file.<br>
</li>
<li>Comments describing copyright and licensing: again, the preferred
form is indicated in the <a href="license_info.html">license
information</a> page<br>
<br>
Note that developers should not provide a copy of
<code>LICENSE_1_0.txt</code> with their libraries: Boost
distributions already include a copy in the Boost root directory.<br>
</li>
<li>A comment line referencing your library on the Boost web site. For
example:<br>
<br>
<code>// See http://www.boost.org/libs/foo/ for library home
page.</code><br>
<br>
where <code>foo</code> is the directory name (see below) for the
library. As well as aiding users who come across a Boost file
detached from its documentation, some of Boost's automatic tools
depend on this comment to identify which library header files belong
to.
</li>
</ul>
</li>
</ul>
<ul>
<li>Make sure your code compiles in the presence of the <code>min()</code>
and <code>max()</code> macros. Some platform headers define
<code>min()</code> and <code>max()</code> macros which cause some common
C++ constructs to fail to compile. Some simple tricks can protect your code
from inappropriate macro substitution:<br>
<ul>
<li>If you want to call <code>std::min()</code> or
<code>std::max()</code>:<br>
<ul>
<li>If you do not require argument-dependent look-up, use
<code>(std::min)(a,b)</code>.
</li>
<li style="list-style: none">
<br>
</li>
<li>If you do require argument-dependent look-up, you should:
</li>
<li style="list-style: none">
<br>
<ul>
<li>
<code>#include <boost/config.hpp></code>
</li>
<li>Use <code>BOOST_USING_STD_MIN();</code> to bring
<code>std::min()</code> into the current scope.
</li>
<li>Use <code>min BOOST_PREVENT_MACRO_SUBSTITUTION
(a,b);</code> to make an argument-dependent call to
<code>min(a,b)</code>.
</li>
</ul>
</li>
</ul>
</li>
<li style="list-style: none">
<br>
</li>
<li>If you want to call
<code>std::numeric_limits<int>::max()</code>, use
<code>(std::numeric_limits<int>::max)()</code> instead.
</li>
<li style="list-style: none">
<br>
</li>
<li>If you want to call a <code>min()</code> or <code>max()</code>
member function, instead to doing <code>obj.min()</code>, use
<code>(obj.min)()</code>.<br>
</li>
<li style="list-style: none">
<br>
</li>
<li>If you want to declare or define a function or a member function
named <code>min</code> or <code>max</code>, then you must use the
<code>BOOST_PREVENT_MACRO_SUBSTITUTION</code> macro. Instead of writing
<code>int min() { return 0; }</code> you should write <code>int min
BOOST_PREVENT_MACRO_SUBSTITUTION () { return 0; }</code><br>
This is true regardless if the function is a free (namespace scope)
function, a member function or a static member function, and it
applies for the function declaration as well as for the function
definition.<br>
</li>
</ul>
</li>
</ul>
<h3>
<a name="Directory_structure" id="Directory_structure">Directory
Structure</a> and Filenames
</h3>
<ul>
<li>File and directory names must contain only <b>lowercase</b> ASCII
letters , numbers, underscores, and a period. Leading character must
be alphabetic. Maximum length 31. Only a single period is permitted.
These requirements ensure file and directory names are relatively portable.
</li>
<li>Files intended to be processed by a C++ compiler as part of a
translation unit should have <b>a three-letter filename extension ending in
"pp"</b>. Other files should <i>not</i> use extensions ending in "pp". This
convention makes it easy to identify all of the C++ source in Boost.
</li>
<li>All libraries have at their highest level a primary directory named for
the particular library. See <a href="#Naming_consistency">Naming
consistency</a>. The primary directory may have sub-directories.
</li>
<li>For very simple libraries implemented entirely within the library
header, all files go in the primary directory (except headers, which go in
the boost header directory).
</li>
</ul>
<blockquote>
<p>
<b>Boost standard sub-directory names</b>
</p>
<table border="1" cellpadding="5">
<tr>
<td>
<b>Sub-directory</b>
</td>
<td>
<b>Contents</b>
</td>
<td>
<b>Required</b>
</td>
</tr>
<tr>
<td>
<code>build</code>
</td>
<td>
Library build files such as a Jamfile.
</td>
<td>
If any build files.
</td>
</tr>
<tr>
<td>
<code>doc</code>
</td>
<td>
Documentation (HTML) files.
</td>
<td>
If several doc files.
</td>
</tr>
<tr>
<td>
<code>example</code>
</td>
<td>
Sample program files.
</td>
<td>
If several sample files.
</td>
</tr>
<tr>
<td>
<code>src</code>
</td>
<td>
Source files which must be compiled to build the library.
</td>
<td>
If any source files.
</td>
</tr>
<tr>
<td>
<code>test</code>
</td>
<td>
Regression or other test programs or scripts.
</td>
<td>
If several test files.
</td>
</tr>
</table>
</blockquote>
<h4>
<a name="Redirection" id="Redirection">Redirection</a>
</h4>
<p>
The primary directory should always contain a file named index.html (or
index.htm). Authors have requested this so that they can publish URL's in
the form <i>http://www.boost.org/libs/lib-name</i> with the assurance a
documentation reorganization won't invalidate the URL. Boost's internal
tools are also simplified by knowing that a library's documentation is
always reachable via the simplified URL.
</p>
<p>
If the documentation is in a doc sub-directory, the primary directory
index.html file should just do an automatic redirection to the doc
subdirectory:
</p>
<blockquote>
<pre>
<html>
<head>
<meta http-equiv="refresh" content="0; URL=doc/index.html">
</head>
<body>
Automatic redirection failed, please go to
<a href="doc/index.html">doc/index.html</a>
</body>
</html>
</pre>
</blockquote>
<h3>
<a name="Naming_consistency">Naming consistency</a>
</h3>
<p>
As library developers and users have gained experience with Boost, the
following consistent naming approach has come to be viewed as very helpful,
particularly for larger libraries that need their own header subdirectories
and namespaces.
</p>
<p>
Here is how it works. The library is given a name that describes the
contents of the library. Cryptic abbreviations are strongly discouraged.
Following the practice of the C++ Standard Library, names are usually
singular rather than plural. For example, a library dealing with file
systems might chose the name "filesystem", but not "filesystems", "fs" or
"nicecode".
</p>
<ul>
<li>The library's primary directory (in parent <i>boost-root/libs</i>) is
given that same name. For example,
<i>boost-root/libs/filesystem</i>.<br>
</li>
<li>The library's primary header directory (in parent
<i>boost-root/boost</i>) is given that same name. For example,
<i>boost-root/boost/filesystem</i>.<br>
</li>
<li>The library's primary namespace (in parent <i>::boost</i>) is given
that same name, except when there's a component with that name (e.g.,
<i>boost::tuple</i>), in which case the namespace name is pluralized. For
example, <i>::boost::filesystem</i>.
</li>
</ul>
<p>
When documenting Boost libraries, follow these conventions (see also the
following section of this document):
</p>
<ul>
<li>The library name is set in roman type.
</li>
<li>The library name is capitalized.
</li>
<li>A period between "Boost" and the library name (e.g., Boost.Bind) is
used if and only if the library name is not followed by the word "library".
</li>
<li>The word "library" is not part of the library name and is therefore
lowercased.
</li>
</ul>
<p>
Here are a few examples of how to apply these conventions:
</p>
<ul>
<li>Boost.Bind was written by Peter Dimov.
</li>
<li>The Boost Bind library was written by Peter Dimov.
</li>
<li>I regularly use Bind, a Boost library written by Peter Dimov.
</li>
</ul>
<h3>
<a name="Documentation" id="Documentation">Documentation</a>
</h3>
<p>
Even the simplest library needs some documentation; the amount should be
proportional to the need. The documentation should assume the readers
have a basic knowledge of C++, but are not necessarily experts.
</p>
<p>
The format for documentation should be HTML, and should not require an
advanced browser or server-side extensions. Style sheets are acceptable.
ECMAScript/JavaScript is not acceptable. The documentation entry point
should always be a file named index.html or index.htm; see <a href=
"#Redirection">Redirection</a>.
</p>
<p>
There is no single right way to do documentation. HTML documentation is
often organized quite differently from traditional printed documents.
Task-oriented styles differ from reference oriented styles. In the end, it
comes down to the question: Is the documentation sufficient for the
mythical "average" C++ programmer to use the library successfully?
</p>
<p>
Appropriate topics for documentation often include:
</p>
<ul>
<li>General introduction to the library.
</li>
<li>Description of each class.
</li>
<li>Relationship between classes.
</li>
<li>For each function, as applicable, description, requirements
(preconditions), effects, post-conditions, returns, and throws.
</li>
<li>Discussion of error detection and recovery strategy.
</li>
<li>How to use including description of typical uses.
</li>
<li>How to compile and link.
</li>
<li>How to test.
</li>
<li>Version or revision history.
</li>
<li>Rationale for design decisions. See <a href=
"#Rationale">Rationale rationale</a>.
</li>
<li>Acknowledgements. See <a href="#Acknowledgements">Acknowledgments
rationale.</a>
</li>
</ul>
<p>
If you need more help with how to write documentation you can check out the
article on <a href="writingdoc/index.html">Writing Documentation for
Boost</a>.
</p>
<h2>
<a name="Rationale" id="Rationale">Rationale</a>
</h2>
<p>
Rationale for some of the requirements and guidelines follows.
</p>
<hr>
<h3>
<a name="Exception-specification" id=
"Exception-specification">Exception-specification</a> rationale
</h3>
<p>
Exception specifications [ISO 15.4] are sometimes coded to indicate what
exceptions may be thrown, or because the programmer hopes they will
improved performance. But consider the following member from a smart
pointer:
</p>
<pre>
T& operator*() const throw() { return *ptr; }
</pre>
<p>
This function calls no other functions; it only manipulates fundamental
data types like pointers Therefore, no runtime behavior of the
exception-specification can ever be invoked. The function is
completely exposed to the compiler; indeed it is declared inline Therefore,
a smart compiler can easily deduce that the functions are incapable of
throwing exceptions, and make the same optimizations it would have made
based on the empty exception-specification. A "dumb" compiler, however, may
make all kinds of pessimizations.
</p>
<p>
For example, some compilers turn off inlining if there is an
exception-specification. Some compilers add try/catch blocks. Such
pessimizations can be a performance disaster which makes the code unusable
in practical applications.
</p>
<p>
Although initially appealing, an exception-specification tends to have
consequences that require <b>very</b> careful thought to understand. The
biggest problem with exception-specifications is that programmers use them
as though they have the effect the programmer would like, instead of the
effect they actually have.
</p>
<p>
A non-inline function is the one place a "throws nothing"
exception-specification may have some benefit with some compilers.
</p>
<hr>
<h3>
<a name="Naming" id="Naming">Naming</a> conventions rationale
</h3>
<p>
The C++ standard committee's Library Working Group discussed this issue in
detail, and over a long period of time. The discussion was repeated again
in early boost postings. A short summary:
</p>
<ul>
<li>Naming conventions are contentious, and although several are widely
used, no one style predominates.
</li>
<li>Given the intent to propose portions of boost for the next revision of
the C++ standard library, boost decided to follow the standard library's
conventions.
</li>
<li>Once a library settles on a particular convention, a vast majority of
stakeholders want that style to be consistently used.
</li>
</ul>
<hr>
<h3>
Source <a name="code_fonts" id="code_fonts">code fonts</a> rationale
</h3>
<p>
Dave Abrahams comments: An important purpose (I daresay the primary
purpose) of source code is communication: the documentation of intent. This
is a doubly important goal for boost, I think. Using a fixed-width font
allows us to communicate with more people, in more ways (diagrams are
possible) right there in the source. Code written for fixed-width fonts
using spaces will read reasonably well when viewed with a variable-width
font, and as far as I can tell every editor supporting variable-width fonts
also supports fixed width. I don't think the converse is true.
</p>
<hr>
<h3>
<a name="Tabs" id="Tabs">Tabs</a> rationale
</h3>
<p>
Tabs are banned because of the practical problems caused by tabs in
multi-developer projects like Boost, rather than any dislike in principle.
See <a href="mailing_lists.htm#archive">mailing list archives</a>. Problems
include maintenance of a single source file by programmers using tabs and
programmers using spaces, and the difficulty of enforcing a consistent tab
policy other than just "no tabs". Discussions concluded that Boost files
should either all use tabs, or all use spaces, and thus the decision to
stick with spaces.
</p>
<hr>
<h3>
ECMAScript/<a name="JavaScript" id="JavaScript">JavaScript</a> rationale
</h3>
<p>
Before the 1.29.0 release, two Boost libraries added ECMAScript/JavaScript
documentation. Controversy followed (see <a href=
"mailing_lists.htm#archive">mailing list archives</a>), and the developers
were asked to remove the ECMAScript/JavaScript. Reasons given for banning
included:
</p>
<ul>
<li>Incompatible with some older browsers and some text based browsers.
</li>
<li>Makes printing docs pages difficult.
</li>
<li>Often results in really bad user interface design.
</li>
<li>"It's just annoying in general."
</li>
<li>Would require Boost to test web pages for ECMAScript/JavaScript
compliance.
</li>
<li>Makes docs maintenance by other than the original developer more
difficult.
</li>
</ul>
<hr>
<h3>
<a name="Rationale_rationale" id="Rationale_rationale">Rationale
rationale</a>
</h3>
<p>
Rationale is defined as "The fundamental reasons for something; basis" by
the American Heritage Dictionary.
</p>
<p>
Beman Dawes comments: Failure to supply contemporaneous rationale for
design decisions is a major defect in many software projects. Lack of
accurate rationale causes issues to be revisited endlessly, causes
maintenance bugs when a maintainer changes something without realizing it
was done a certain way for some purpose, and shortens the useful lifetime
of software.
</p>
<p>
Rationale is fairly easy to provide at the time decisions are made, but
very hard to accurately recover even a short time later.
</p>
<hr>
<h3>
<a name="Acknowledgements" id="Acknowledgements">Acknowledgements</a>
rationale
</h3>
<p>
As a library matures, it almost always accumulates improvements suggested
to the authors by other boost members. It is a part of the culture of
boost.org to acknowledge such contributions, identifying the person making
the suggestion. Major contributions are usually acknowledged in the
documentation, while minor fixes are often mentioned in comments within the
code itself.
</p>
<hr>
<p>
Revised
<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->
04 November, 2003<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p>
© <a name="Copyright" id="Copyright">Copyright</a> Beman Dawes 2003.
</p>
<p>
Distributed under the Boost Software License, Version 1.0. (See
accompanying file <a href="../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or copy
at <a href=
"http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)
</p>
</body>
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