StackOverflow2013

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copied!<p>A block winds up being an instance of type <code>__NSGlobalBlock__</code>, as seen in the following snippet:</p> <pre> void (^aBlock)(void) = ^(void) { NSLog(@"Hello world"); }; // prints "type = __NSGlobalBlock__" NSLog(@"type = %@", [aBlock class]); </pre> <p>In order to create a category of a class, the compiler needs to be able to see the original <code>@interface</code> declaration of the class. I can't find the declaration for <code>__NSGlobalBlock__</code> and probably for good reason.</p> <p><a href="http://cocoawithlove.com/2009/10/how-blocks-are-implemented-and.html" rel="nofollow">This article</a> and <a href="http://www.mikeash.com/pyblog/friday-qa-2009-08-14-practical-blocks.html" rel="nofollow">this article</a> contain some useful information about the implementation of blocks.</p> <p>To your original point, why not just make a category of <code>NSArray</code> for your <code>mapTo</code> method? It seems like a better place for that sort of functionality.</p> <p><em>Updated</em></p> <p>Let's say you <em>can</em> add a category to the Block object. How would you invoke the block from the category's method? To the best of my understanding, the only way to invoke a block is via the <code>()</code> operator (e.g., <code>aBlock()</code>). I don't think there's a way to tell from the Block object the number and types of parameters. So, what arguments would you pass in to the block invocation?</p> <p>I'm not recommending you do this, but the following works...</p> <pre> @interface NSObject (BlockExtension) - (void)foo; @end @implementation NSObject (BlockExtension) - (void)foo { // not sure how else to determine if self is a Block since neither // __NSGlobalBlock__ nor any of its superclasses (except NSObject) // are accessible to the compiler if ([[[self class] description] isEqual:@"__NSGlobalBlock__"]) { NSLog(@"foo"); // now what? // can't call self(), it doesn't compile // how else can I invoke this block? } } @end ... void (^aBlock)(void) = ^(void) { NSLog(@"Hello world"); }; // prints "foo" [aBlock foo]; </pre>

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