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author | Mike Pall <mike> | 2011-11-11 20:41:44 +0100 |
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committer | Mike Pall <mike> | 2011-11-11 20:41:44 +0100 |
commit | 0123e4fc895f4a52422dff05a29596e389b4749c (patch) | |
tree | e67a1c9bda90a721212973c204f357f4b7a2456b /doc/ext_ffi_tutorial.html | |
parent | fa1675baad93dbe503d834eb380b2a8efdf301fe (diff) | |
download | luajit2-0123e4fc895f4a52422dff05a29596e389b4749c.tar.gz |
FFI: Extend metamethod tutorial.
Diffstat (limited to 'doc/ext_ffi_tutorial.html')
-rw-r--r-- | doc/ext_ffi_tutorial.html | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/doc/ext_ffi_tutorial.html b/doc/ext_ffi_tutorial.html index 9349aea4..fb46a842 100644 --- a/doc/ext_ffi_tutorial.html +++ b/doc/ext_ffi_tutorial.html @@ -15,6 +15,7 @@ span.mark { color: #4040c0; font-family: Courier New, Courier, monospace; pre.mark { padding-left: 2em; } table.idiomtable { line-height: 1.2; } table.idiomtable tt { font-size: 100%; } +table.idiomtable td { vertical-align: top; } tr.idiomhead td { font-weight: bold; } td.idiomc { width: 12em; } td.idiomlua { width: 14em; } @@ -454,7 +455,7 @@ the origin. <span class="mark">④</span> If we run out of operators, we can define named methods, too. Here the <tt>__index</tt> table defines an <tt>area</tt> function. For custom indexing needs, one might want to -define <tt>__index</tt> and <tt>__newindex</tt> functions instead. +define <tt>__index</tt> and <tt>__newindex</tt> <em>functions</em> instead. </p> <p> <span class="mark">⑤</span> This associates the metamethods with @@ -478,6 +479,24 @@ defined metamethods. Note that <tt>area</tt> is a method and must be called with the Lua syntax for methods: <tt>a:area()</tt>, not <tt>a.area()</tt>. </p> +<p> +The C type metamethod mechanism is most useful when used in +conjunction with C libraries that are written in an object-oriented +style. Creators return a pointer to a new instance and methods take an +instance pointer as the first argument. Sometimes you can just point +<tt>__index</tt> to the library namespace and <tt>__gc</tt> to the +destructor and you're done. But often enough you'll want to add +convenience wrappers, e.g. to return actual Lua strings or when +returning multiple values. +</p> +<p> +Some C libraries only declare instance pointers as an opaque +<tt>void *</tt> type. In this case you can use a fake type for all +declarations, e.g. a pointer to a named (incomplete) struct will do: +<tt>typedef struct foo_type *foo_handle</tt>. The C side doesn't +know what you declare with the LuaJIT FFI, but as long as the underlying +types are compatible, everything still works. +</p> <h2 id="idioms">Translating C Idioms</h2> <p> |