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    <p>The only nice discussion I know is at Mike Ash's <a href="http://mikeash.com/pyblog//friday-qa-2009-03-27-objective-c-message-forwarding.html">blog post</a>. It's not that hard, actually. </p> <p>I once needed to split a big <code>NSManagedObject</code> subclass into two, but decided to keep the fact an implementation detail so that I don't have to rewrite other parts of my app. So, I needed to synthesize getter and setter which sends <code>[self foo]</code> to <code>[self.data foo]</code>, automatically. </p> <p>To achieve that, I did the following:</p> <ol> <li><p>Prepare the new method, already in my class.</p> <pre><code>- (id)_getter_ { return objc_msgSend(self.data, _cmd); } - (void)_setter_:(id)value { objc_msgSend(self.data, _cmd,value); } </code></pre> <p>Note that <code>_cmd</code> has the selector in it. So, usually, <code>_cmd</code> is either <code>@selector(_getter_)</code> or <code>@selector(_setter_)</code> in these methods, but I'm going to plug the implementation of <code>_getter_</code> as the implementation of <code>foo</code>. Then, <code>_cmd</code> contains <code>@selector(foo)</code>, and thus calls <code>self.data</code>'s <code>foo</code>.</p></li> <li><p>Write a generic synthesizing method:</p> <pre><code>+(void)synthesizeForwarder:(NSString*)getterName { NSString*setterName=[NSString stringWithFormat:@"set%@%@:", [[getterName substringToIndex:1] uppercaseString],[getterName substringFromIndex:1]]; Method getter=class_getInstanceMethod(self, @selector(_getter_)); class_addMethod(self, NSSelectorFromString(getterName), method_getImplementation(getter), method_getTypeEncoding(getter)); Method setter=class_getInstanceMethod(self, @selector(_setter_:)); class_addMethod(self, NSSelectorFromString(setterName), method_getImplementation(setter), method_getTypeEncoding(setter)); } </code></pre> <p>Note that this is a class method. So <code>self</code> stands for the class. Note also that I didn't hardcode type encodings (which tells Objective-C runtime what the arguments of the particular method are). The syntax of type encodings is documented, but constructing by hand is very error-prone; I wasted a few days that way until Mike Ash told me to stop it. Generate it using an existing method.</p></li> <li><p>Generate forwarders at the earliest possible time:</p> <pre><code> +(void)load { for(NSString*selectorName in [NSArray arrayWithObjects:@"foo", @"bar", @"baz",nil]){ [self synthesizeForwarder:selectorName]; } } </code></pre> <p>This generates <code>foo</code>, <code>setFoo:</code>, <code>bar</code>, <code>setBar:</code>, and <code>baz</code>, <code>setBaz:</code>.</p></li> </ol> <p>Hope this helps!</p>
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    1. COAwesome. Thanks for the great and quick response!
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