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POARC and Message Forwarding
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  1. POARC and Message Forwarding
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    copied!<p>I tried to implement Message Forwarding. Xcode 5, ARC is ON, new default iPhone project. <a href="https://developer.apple.com/library/mac/documentation/cocoa/conceptual/ObjCRuntimeGuide/Articles/ocrtForwarding.html" rel="nofollow">I read a documentation here</a> </p> <p>I have two custom classes in my project: <code>Hello</code> and <code>World</code>.</p> <pre><code>#import &lt;Foundation/Foundation.h&gt; @interface Hello : NSObject - (void) say; @end #import "Hello.h" #import "World.h" @implementation Hello - (void) say { NSLog(@"hello!"); } -(void)forwardInvocation:(NSInvocation *)invocation { NSLog(@"forward invocation"); World *w = [[World alloc] init]; if ([w respondsToSelector:[invocation selector]]) { [invocation invokeWithTarget:w]; } else { [self doesNotRecognizeSelector: [invocation selector]]; } } -(NSMethodSignature*)methodSignatureForSelector:(SEL)selector { NSLog(@"method signature"); NSMethodSignature *signature = [super methodSignatureForSelector:selector]; if (! signature) { World *w = [[World alloc] init]; signature = [w methodSignatureForSelector:selector]; } return signature; } @end </code></pre> <p>World is simple:</p> <pre><code>#import &lt;Foundation/Foundation.h&gt; @interface World : NSObject - (void) spin; @end #import "World.h" @implementation World - (void) spin { NSLog(@"spin around"); } @end </code></pre> <p>In my AppDelegate i wrote three simple lines:</p> <pre><code>Hello *me = [[Hello alloc] init]; [me say]; [me spin]; </code></pre> <p>And compiler give me an error: <code>AppDelegate.m:23:9: No visible @interface for 'Hello' declares the selector 'spin'</code> and doesn't build a project. When I retype it: <code>[me performSelector:@selector(spin)];</code> - it works fine.</p> <p>Code <code>[me spin]</code> works when ARC is OFF only (but compiler generates a warning <code>AppDelegate.m:23:9: 'Hello' may not respond to 'spin'</code>).</p> <p>My questions: why? and How can I use ARC with message forwarding?</p>
 

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