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96 lines
4.2 KiB
HTML
96 lines
4.2 KiB
HTML
4 years ago
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<title>Dynamically registering methods - Using the GNU Compiler Collection (GCC)</title>
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<link rel="up" href="Messaging-with-the-GNU-Objective_002dC-runtime.html#Messaging-with-the-GNU-Objective_002dC-runtime" title="Messaging with the GNU Objective-C runtime">
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<link rel="next" href="Forwarding-hook.html#Forwarding-hook" title="Forwarding hook">
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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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<div class="node">
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<a name="Dynamically-registering-methods"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Forwarding-hook.html#Forwarding-hook">Forwarding hook</a>,
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Up: <a rel="up" accesskey="u" href="Messaging-with-the-GNU-Objective_002dC-runtime.html#Messaging-with-the-GNU-Objective_002dC-runtime">Messaging with the GNU Objective-C runtime</a>
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<hr>
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</div>
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<h4 class="subsection">8.10.1 Dynamically Registering Methods</h4>
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<p>If <code>objc_msg_lookup()</code> does not find a suitable method
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implementation, because the receiver does not implement the required
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method, it tries to see if the class can dynamically register the
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method.
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<p>To do so, the runtime checks if the class of the receiver implements
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the method
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<pre class="smallexample"> + (BOOL) resolveInstanceMethod: (SEL)selector;
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</pre>
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<p>in the case of an instance method, or
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<pre class="smallexample"> + (BOOL) resolveClassMethod: (SEL)selector;
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</pre>
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<p>in the case of a class method. If the class implements it, the
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runtime invokes it, passing as argument the selector of the original
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method, and if it returns <code>YES</code>, the runtime tries the lookup
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again, which could now succeed if a matching method was added
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dynamically by <code>+resolveInstanceMethod:</code> or
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<code>+resolveClassMethod:</code>.
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<p>This allows classes to dynamically register methods (by adding them to
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the class using <code>class_addMethod</code>) when they are first called.
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To do so, a class should implement <code>+resolveInstanceMethod:</code> (or,
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depending on the case, <code>+resolveClassMethod:</code>) and have it
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recognize the selectors of methods that can be registered dynamically
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at runtime, register them, and return <code>YES</code>. It should return
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<code>NO</code> for methods that it does not dynamically registered at
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runtime.
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<p>If <code>+resolveInstanceMethod:</code> (or <code>+resolveClassMethod:</code>) is
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not implemented or returns <code>NO</code>, the runtime then tries the
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forwarding hook.
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<p>Support for <code>+resolveInstanceMethod:</code> and
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<code>resolveClassMethod:</code> was added to the GNU Objective-C runtime in
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GCC version 4.6.
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<!-- ========================================================================= -->
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