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86 lines
3.8 KiB
HTML
86 lines
3.8 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Messaging with the GNU Objective-C runtime - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Objective_002dC.html#Objective_002dC" title="Objective-C">
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<link rel="prev" href="Fast-enumeration.html#Fast-enumeration" title="Fast enumeration">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Messaging-with-the-GNU-Objective-C-runtime"></a>
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<a name="Messaging-with-the-GNU-Objective_002dC-runtime"></a>
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<p>
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Previous: <a rel="previous" accesskey="p" href="Fast-enumeration.html#Fast-enumeration">Fast enumeration</a>,
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Up: <a rel="up" accesskey="u" href="Objective_002dC.html#Objective_002dC">Objective-C</a>
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<hr>
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</div>
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<h3 class="section">8.10 Messaging with the GNU Objective-C Runtime</h3>
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<p>This section is specific for the GNU Objective-C runtime. If you are
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using a different runtime, you can skip it.
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<p>The implementation of messaging in the GNU Objective-C runtime is
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designed to be portable, and so is based on standard C.
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<p>Sending a message in the GNU Objective-C runtime is composed of two
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separate steps. First, there is a call to the lookup function,
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<code>objc_msg_lookup ()</code> (or, in the case of messages to super,
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<code>objc_msg_lookup_super ()</code>). This runtime function takes as
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argument the receiver and the selector of the method to be called; it
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returns the <code>IMP</code>, that is a pointer to the function implementing
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the method. The second step of method invocation consists of casting
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this pointer function to the appropriate function pointer type, and
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calling the function pointed to it with the right arguments.
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<p>For example, when the compiler encounters a method invocation such as
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<code>[object init]</code>, it compiles it into a call to
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<code>objc_msg_lookup (object, @selector(init))</code> followed by a cast
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of the returned value to the appropriate function pointer type, and
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then it calls it.
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<ul class="menu">
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<li><a accesskey="1" href="Dynamically-registering-methods.html#Dynamically-registering-methods">Dynamically registering methods</a>
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<li><a accesskey="2" href="Forwarding-hook.html#Forwarding-hook">Forwarding hook</a>
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</ul>
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<!-- ========================================================================= -->
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</body></html>
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