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<h4 class="subsection">8.10.1 Dynamically Registering Methods</h4>
<p>If <code>objc_msg_lookup()</code> does not find a suitable method
implementation, because the receiver does not implement the required
method, it tries to see if the class can dynamically register the
method.
<p>To do so, the runtime checks if the class of the receiver implements
the method
<pre class="smallexample"> + (BOOL) resolveInstanceMethod: (SEL)selector;
</pre>
<p>in the case of an instance method, or
<pre class="smallexample"> + (BOOL) resolveClassMethod: (SEL)selector;
</pre>
<p>in the case of a class method. If the class implements it, the
runtime invokes it, passing as argument the selector of the original
method, and if it returns <code>YES</code>, the runtime tries the lookup
again, which could now succeed if a matching method was added
dynamically by <code>+resolveInstanceMethod:</code> or
<code>+resolveClassMethod:</code>.
<p>This allows classes to dynamically register methods (by adding them to
the class using <code>class_addMethod</code>) when they are first called.
To do so, a class should implement <code>+resolveInstanceMethod:</code> (or,
depending on the case, <code>+resolveClassMethod:</code>) and have it
recognize the selectors of methods that can be registered dynamically
at runtime, register them, and return <code>YES</code>. It should return
<code>NO</code> for methods that it does not dynamically registered at
runtime.
<p>If <code>+resolveInstanceMethod:</code> (or <code>+resolveClassMethod:</code>) is
not implemented or returns <code>NO</code>, the runtime then tries the
forwarding hook.
<p>Support for <code>+resolveInstanceMethod:</code> and
<code>resolveClassMethod:</code> was added to the GNU Objective-C runtime in
GCC version 4.6.
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