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PORetaining mutable variables in blocks without causing retain cycles in Objective-C
 

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    <p>I'm using blocks to handle the response of async http requests in a non-ARC project. The code looks like this (the relevant parts):</p> <pre><code>NSMutableUrlRequest* request = ...; __block typeof(self) mutableSelf = self; void (^didGetSessionBlock)(Gopher* newGopher) = ^(Gopher* newGopher) { if (newGopher.statusCode == HTTP_OK) { ... mutableSelf.retryOnFail = NO; [mutableSelf executeRequest:request]; } ... [mutableSelf setStatusCode:newGopher.statusCode]; }; Gopher* newGopher = [[[Gopher alloc] init] autorelease]; [newGopher setDidCompleteBlock:didGetSessionBlock]; [newGopher fetchSession:myApp.settings.userName password:myApp.settings.password]; </code></pre> <p><code>__block mutableSelf</code> is used so that I can modify <code>self</code> inside of the block (and not a copy of <code>self</code>). The <code>__block</code> keyword, if I understand correctly, also has the effect that <code>mutableSelf</code> is not retained so it might already be released when the block is executing (and this is exactly what happens).</p> <p>If I change </p> <pre><code>[mutableSelf executeRequest:request]; </code></pre> <p>to </p> <pre><code>[self executeRequest:request]; </code></pre> <p>all is well since <code>self</code> gets retained and won't be released until the block has executed. However, directly referencing self might cause leaks due to retain cycles.</p> <p>Is there a way around this? Should I manually retain <code>mutableSelf</code> when it's declared and then release it inside of the block? Or should I use <code>self</code> inside the block where I'm not modifying it, potentially creating a leak? Both variants seem fragile and need explanations in comments to avoid confusion and future bugs if/when the code is modified.</p> <p>Is there a way to solve this problem? If not, what is the best approach?</p>
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    1. COYou might like to have a look at [Retain cycle on self with Blocks](http://stackoverflow.com/questions/4352561/retain-cycle-on-self-with-blocks) and its answers.
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      1. USJosh Caswell
 

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