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copied!<p>As far as I know, <code>strong</code> and <code>retain</code> are synonyms, so they do <em>exactly</em> the same.</p> <p>Then the <code>weak</code> is almost like <code>assign</code>, but automatically set to nil after the object, it is pointing to, is deallocated.</p> <p><strong>That means, you can simply replace them.</strong></p> <p><strong>However</strong>, there is one special case I've encountered, where I had to use <code>assign</code>, rather than <code>weak</code>. Let's say we have two properties <code>delegateAssign</code> and <code>delegateWeak</code>. In both is stored our delegate, that is owning us by having the only strong reference. The delegate is deallocating, so our <code>-dealloc</code> method is called too.</p> <pre><code>// Our delegate is deallocating and there is no other strong ref. - (void)dealloc { [delegateWeak doSomething]; [delegateAssign doSomething]; } </code></pre> <p>The delegate is already in deallocation process, but still not fully deallocated. The problem is that <strong><code>weak</code> references to him are already nullified!</strong> Property <code>delegateWeak</code> contains nil, but <code>delegateAssign</code> contains valid object (with all properties already released and nullified, but still valid).</p> <pre><code>// Our delegate is deallocating and there is no other strong ref. - (void)dealloc { [delegateWeak doSomething]; // Does nothing, already nil. [delegateAssign doSomething]; // Successful call. } </code></pre> <p>It is quite special case, but it reveal us how those <code>weak</code> variables work and when they are nullified.</p>

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