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POClarification on Apple's Block Docs?
 

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    <p>I am working through some retain-cycle issues with blocks/ARC, and I am trying to get my head around the nuances. Any guidance is appreciated.</p> <p>Apple's documentation on "Blocks and Variables" (http://developer.apple.com/library/ios/#documentation/cocoa/Conceptual/Blocks/Articles/bxVariables.html) says the following:</p> <blockquote> <p>If you use a block within the implementation of a method, the rules for memory management of object instance variables are more subtle:</p> <p>If you access an instance variable by reference, self is retained; If you access an instance variable by value, the variable is retained. The following examples illustrate the two different situations:</p> </blockquote> <pre><code>dispatch_async(queue, ^{ // instanceVariable is used by reference, self is retained doSomethingWithObject(instanceVariable); }); id localVariable = instanceVariable; dispatch_async(queue, ^{ // localVariable is used by value, localVariable is retained (not self) doSomethingWithObject(localVariable); }); </code></pre> <p>I find this explanation confusing.</p> <ol> <li>Is this appropriate use of the "by value" / "by reference" terminology? Assuming that these variables are of the same type (id), it seems like the distinguishing characteristic between them is their scope.</li> <li><p>I do not see how self is being referenced in the "by reference" example? If an accessor method were being used, (e.g. - below), I could see self being retained.</p> <p>doSomethingWithObject(self.instanceVariable);</p></li> <li><p>Do you have any guidance on when one might want to do things one way or the other?</p></li> <li>If conventional wisdom is to utilize the "by value" variables, it seems like this is going to result in a lot of additional code for additional variable declarations?</li> <li>In a circumstance where nested blocks are coming into play, it seems like it may be more maintainable to avoid declaring the blocks inside of each other as one could ultimately end up with a potpourri of unintentionally retained objects?</li> </ol>
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