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FFI: Extend metamethod tutorial.

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Mike Pall 2011-11-11 20:41:44 +01:00
parent fa1675baad
commit 0123e4fc89
1 changed files with 20 additions and 1 deletions
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doc/ext_ffi_tutorial.html
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@ -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">&#9315;</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">&#9316;</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&nbsp;type metamethod mechanism is most useful when used in
conjunction with C&nbsp;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&nbsp;*</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&nbsp;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&nbsp;Idioms</h2>
<p>