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    <p>One way to reduce nesting is to define methods that return the individual blocks. In order to facilitate the data sharing which is done "auto-magically" by the Objective C compiler through closures, you would need to define a separate class to hold the shared state.</p> <p>Here is a rough sketch of how this can be done:</p> <pre><code>typedef void (^WithStatus)(int); @interface AsyncHandler : NSObject { NSString *_sharedString; NSURL *_innerUrl; NSURL *_middleUrl; WithStatus _innermostBlock; } +(void)handleRequest:(WithStatus)innermostBlock outerUrl:(NSURL*)outerUrl middleUrl:(NSURL*)middleUrl innerUrl:(NSURL*)innerUrl; -(WithStatus)outerBlock; -(WithStatus)middleBlock; @end @implementation AsyncHandler +(void)handleRequest:(WithStatus)innermostBlock outerUrl:(NSURL*)outerUrl middleUrl:(NSURL*)middleUrl innerUrl:(NSURL*)innerUrl { AsyncHandler *h = [[AsyncHandler alloc] init]; h-&gt;_innermostBlock = innermostBlock; h-&gt;_innerUrl = innerUrl; h-&gt;_middleUrl = middleUrl; [remoteAPIWithURL:outerUrl success:[self outerBlock]]; } -(WithStatus)outerBlock { return ^(int success) { _sharedString = [NSString stringWithFormat:@"Outer: %i", success]; [remoteAPIWithURL:_middleUrl success:[self middleBlock]]; }; } -(WithStatus)middleBlock { return ^(int success) { NSLog("Shared string: %@", _sharedString); [remoteAPIWithURL:_innerUrl success:_innermostBlock]; }; } @end </code></pre> <p>Note: All of this assumes ARC; if you are compiling without it, you need to use <a href="https://stackoverflow.com/a/2659357/335858"><code>Block_copy</code></a> in the methods returning blocks. You would also need to do a copy in the calling code below.</p> <p>Now your original function can be re-written without the <a href="http://en.wikipedia.org/wiki/Matryoshka_doll" rel="nofollow noreferrer">"Russian doll"</a> nesting, like this:</p> <pre><code>[AsyncHandler handleRequest:^(int status){ //succes!!! } outerUrl:[NSURL @"http://my.first.url.com"] middleUrl:[NSURL @"http://my.second.url.com"] innerUrl:[NSURL @"http://my.third.url.com"] ]; </code></pre>
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    1. POHow to do structured programming using blocks in Objective-C
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    1. COI did not try any of it, so there is a good chance that this code would not compile. If that is the case, please let me know, and I'll try fixing it.
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    2. COAlthough I agree this solves the particular example of me fetching 3 urls, it would need a new class for fetching 4 or 5 urls, or any other intricate async flow. I do like that you've encapsulated the complexity in an easy to use class though
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    3. CO@Toad Correct, this approach is usable to encapsulate one particular flow, and does not offer a framework-like ability to compose flows arbitrarily. The idea was to make your asynchronous code more manageable while keeping it understandable without much prior knowledge.
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