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113 lines
5.2 KiB
HTML
113 lines
5.2 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 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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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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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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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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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="Messaging with the GNU Objective-C runtime (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Messaging with the GNU Objective-C runtime (Using the GNU Compiler Collection (GCC))">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Objective_002dC.html#Objective_002dC" rel="up" title="Objective-C">
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<link href="Dynamically-registering-methods.html#Dynamically-registering-methods" rel="next" title="Dynamically registering methods">
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<link href="Fast-enumeration-protocol.html#Fast-enumeration-protocol" rel="prev" title="Fast enumeration protocol">
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<style type="text/css">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Messaging-with-the-GNU-Objective_002dC-runtime"></a>
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<div class="header">
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<p>
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Previous: <a href="Fast-enumeration.html#Fast-enumeration" accesskey="p" rel="prev">Fast enumeration</a>, Up: <a href="Objective_002dC.html#Objective_002dC" accesskey="u" rel="up">Objective-C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Messaging-with-the-GNU-Objective_002dC-Runtime"></a>
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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>
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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>
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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>
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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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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Dynamically-registering-methods.html#Dynamically-registering-methods" accesskey="1">Dynamically registering methods</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Forwarding-hook.html#Forwarding-hook" accesskey="2">Forwarding hook</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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</table>
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</body>
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</html>
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