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POARC and bridged cast
 

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    <p>With ARC, I can no longer cast <code>CGColorRef</code> to <code>id</code>. I learned that I need to do a bridged cast. According <a href="http://clang.llvm.org/docs/AutomaticReferenceCounting.html#bridged-casts" rel="noreferrer">clang docs</a>:</p> <blockquote> <p>A <strong>bridged cast</strong> is a C-style cast annotated with one of three keywords:</p> <p><code>(__bridge T) op</code> casts the operand to the destination type <code>T</code>. If <code>T</code> is a retainable object pointer type, then <code>op</code> must have a non-retainable pointer type. If <code>T</code> is a non-retainable pointer type, then op must have a retainable object pointer type. Otherwise the cast is ill-formed. There is no transfer of ownership, and ARC inserts no retain operations.</p> <p><code>(__bridge_retained T) op</code> casts the operand, which must have retainable object pointer type, to the destination type, which must be a non-retainable pointer type. ARC retains the value, subject to the usual optimizations on local values, and the recipient is responsible for balancing that +1.</p> <p><code>(__bridge_transfer T) op</code> casts the operand, which must have non-retainable pointer type, to the destination type, which must be a retainable object pointer type. ARC will release the value at the end of the enclosing full-expression, subject to the usual optimizations on local values.</p> <p>These casts are required in order to transfer objects in and out of ARC control; see the rationale in the section on conversion of retainable object pointers.</p> <p>Using a <code>__bridge_retained</code> or <code>__bridge_transfer</code> cast purely to convince ARC to emit an unbalanced retain or release, respectively, is poor form.</p> </blockquote> <p>In what kind of situations would I use each?</p> <p>For example, <code>CAGradientLayer</code> has a <code>colors</code> property which accepts an array of <code>CGColorRef</code>s. My guess is that I should use <code>__brige</code> here, but exactly why I should (or should not) is unclear.</p>
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    1. COHave you watched WWDC 2011 session 323 yet? That explains ARC far better than I could here. It covers all the details from beginning to end. It's a must see session for every Mac/iOS developer.
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    2. COThanks, I will take a look at it.
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