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    <blockquote> <p>Why does this snippet of code work?</p> </blockquote> <p>The first snipped is working because the block implementation has no reference to the surrounding scope, and it's therefore configured by clang as a <strong><em>global</em></strong> block. This causes the block not to be on the stack as it would normally be.</p> <blockquote> <p>myBlock should be destroyed.</p> </blockquote> <p>Stack frames (and their local variable) don't get <em>destroyed</em>. Their memory is made available for further allocation. Anyway, due to the simplicity of your example, you're getting a global block which doesn't live on the stack frame.</p> <p>If you were making any reference to the surrounding scope you would have had a stack-based block and <code>myBlock</code> would have been a dangling pointer to an on-owned memory location, likely leading to a crash.</p> <blockquote> <p><code>[obj retainCount]</code> in block prints 1 instead 2, why?</p> </blockquote> <p>Sounds reasonable.</p> <p>You are allocating an object (retain count: 1), the block is retaining it (retain count: 2), you are releasing it (retain count: 1), the block is eventually executed (retain count still 1).</p> <p>As a general note, anyway, don't rely upon <code>retainCount</code> when reasoning about memory. The memory management process has a lot going on under the hood, and you cannot definitely say anything only by looking at the value of <code>retainCount</code>, due to internal details of the implementation that you cannot possibly take into account. More on the subject here: <a href="http://whentouseretaincount.com/" rel="nofollow">http://whentouseretaincount.com/</a></p>
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    1. POLifecycle of blocks in Objective-C
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    1. USGabriele Petronella
    1. USGabriele Petronella
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    1. COThanks for the explanation about retainCount
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      1. USVladimir
    2. COThe first code snippet doesn't work by coincidence. Try to push on the stack a variable as big as enough to overwrite the memory where the supposed stack block is allocated, the code will still work. Because the block is global, not on the stack.
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      1. USRamy Al Zuhouri
    3. CO@Ramy I stand corrected. Modified my answer, thank you
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      1. USGabriele Petronella
 

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