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    <ol> <li><p><em><strong>Is this appropriate use of the "by value" / "by reference" terminology?</em></strong> It's at least analogous to the typical use. Copying a value to a local variable is like copying a value onto the stack; using an ivar is like passing a pointer to a value that's stored somewhere else.</p></li> <li><p><em><strong>I do not see how self is being referenced in the "by reference" example?</em></strong> When you use an instance variable inside a method, the reference to <code>self</code> is implied. Some people actually write <code>self-&gt;foo</code> instead of <code>foo</code> to access an ivar just to remind themselves that <code>foo</code> is an ivar. I don't recommend that, but the point is that <code>foo</code> and <code>self-&gt;foo</code> mean the same thing. If you access an ivar inside a block, <code>self</code> will be retained in order to ensure that the ivar is preserved for the duration of the block.</p></li> <li><p><em><strong>Do you have any guidance on when one might want to do things one way or the other?</em></strong> It's useful to think in terms of the pass by reference/pass by value distinction here. As AliSoftware explained local variables are preserved when the block is created, just as parameters passed by value are copied when a function is called. An ivar is accessed through self just as a parameter passed by reference is accessed through a pointer, so its value isn't determined until you actually use it.</p></li> <li><p><em><strong>it seems like this is going to result in a lot of additional code for additional variable declarations?</em></strong> Blocks have been a feature of the language for a while now, and I haven't noticed that this is a problem. More often, you want the opposite behavior: a variable declared locally that you can modify within a block (or several blocks). The <code>__block</code> storage type makes that possible.</p></li> <li><p><em><strong>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?</em></strong> There's nothing wrong with letting one or more blocks retain an object for as long as they need it -- the object will be released just as soon as the blocks that use it terminate. This fits perfectly with the usual Objective-c manual memory management philosophy, where every object worries only about balancing its own retains. A better reason to avoid several layers of nested blocks is that that sort of code may be more difficult to understand than it needs to be.</p></li> </ol>
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