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    <p>For posterity / completeness's sake… Here are two FULL examples of how to implement this ridiculously versatile "way of doing things". @Robert's answer is blissfully concise and correct, but here I want to also show ways to actually "define" the blocks. </p> <pre><code>@interface ReusableClass : NSObject @property (nonatomic,copy) CALayer*(^layerFromArray)(NSArray*); @end @implementation ResusableClass static NSString const * privateScope = @"Touch my monkey."; - (CALayer*(^)(NSArray*)) layerFromArray { return ^CALayer*(NSArray* array){ CALayer *returnLayer = CALayer.layer for (id thing in array) { [returnLayer doSomethingCrazy]; [returnLayer setValue:privateScope forKey:@"anticsAndShenanigans"]; } return list; }; } @end </code></pre> <p>Silly? <em>Yes.</em> Useful? <strong><em>Hells yeah.</em></strong> Here is a different, "more atomic" way of setting the property.. and a class that is ridiculously useful…</p> <pre><code>@interface CALayoutDelegator : NSObject @property (nonatomic,strong) void(^layoutBlock)(CALayer*); @end @implementation CALayoutDelegator - (id) init { return self = super.init ? [self setLayoutBlock: ^(CALayer*layer){ for (CALayer* sub in layer.sublayers) [sub someDefaultLayoutRoutine]; }], self : nil; } - (void) layoutSublayersOfLayer:(CALayer*)layer { self.layoutBlock ? self.layoutBlock(layer) : nil; } @end </code></pre> <p>This illustrates setting the block property via the accessor (albeit inside init, a debatably dicey practice..) vs the first example's "nonatomic" "getter" mechanism. In either case… the "hardcoded" implementations can always be overwritten, <em>per instance</em>.. a lá..</p> <pre><code>CALayoutDelegator *littleHelper = CALayoutDelegator.new; littleHelper.layoutBlock = ^(CALayer*layer){ [layer.sublayers do:^(id sub){ [sub somethingElseEntirely]; }]; }; someLayer.layoutManager = littleHelper; </code></pre> <p>Also.. if you want to add a block property in a category... say you want to use a Block instead of some old-school target / action "action"... You can just use associated values to, well.. associate the blocks.</p> <pre><code>typedef void(^NSControlActionBlock)(NSControl*); @interface NSControl (ActionBlocks) @property (copy) NSControlActionBlock actionBlock; @end @implementation NSControl (ActionBlocks) - (NSControlActionBlock) actionBlock { // use the "getter" method's selector to store/retrieve the block! return objc_getAssociatedObject(self, _cmd); } - (void) setActionBlock:(NSControlActionBlock)ab { objc_setAssociatedObject( // save (copy) the block associatively, as categories can't synthesize Ivars. self, @selector(actionBlock),ab ,OBJC_ASSOCIATION_COPY); self.target = self; // set self as target (where you call the block) self.action = @selector(doItYourself); // this is where it's called. } - (void) doItYourself { if (self.actionBlock &amp;&amp; self.target == self) self.actionBlock(self); } @end </code></pre> <p>Now, when you make a button, you don't have to set up some <code>IBAction</code> drama.. Just associate the work to be done at creation... </p> <pre><code>_button.actionBlock = ^(NSControl*thisButton){ [doc open]; [thisButton setEnabled:NO]; }; </code></pre> <p>This pattern can be applied <em>OVER and OVER to</em> Cocoa API's. Use properties to bring the relevant parts of your code <em>closer together</em>, eliminate <em>convoluted delegation paradigms</em>, and leverage the power of objects beyond that of just acting as dumb "containers".</p>
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