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PONSCopyObject considered harmful?
 

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    <p>In the Xcode documentation for <a href="http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Functions/Reference/reference.html#//apple_ref/c/func/NSCopyObject" rel="nofollow noreferrer"><code>NSCopyObject</code></a>, the special considerations section states:</p> <blockquote> <p>This function is dangerous and very difficult to use correctly. It's use as part of <code>copyWithZone:</code> by any class that can be subclassed, is highly error prone. Under GC or when using Objective-C 2.0, the zone is completely ignored.</p> <p>This function is likely to be deprecated after Mac OS X 10.6.</p> </blockquote> <p>Why is it difficult to use correctly? It performs a shallow (bit-for-bit) copy. Objects are not copied or retained. The documentation is pretty clear on this.</p> <p>If I'm not missing other reasons, what is the preferred alternative for performing a shallow copy of an object?</p> <p><strong>Edit:</strong></p> <p>There are valid reasons to want to perform a shallow copy. One example: a class may have many instance variables, most of which are primitive types (integer, float) or objects that are intentionally not retained to avoid retain cycles (delegates). A shallow copy using <code>NSCopyObject</code> copies all of these in one nice, self-documenting line of code. Any remaining ivars that do need to be reference counted can be retained or copied individually.</p> <p>The alternative to this is to either assign to the new object using pointer syntax (<code>newObject-&gt;ivar = ivar</code>) or to create an init method with a potentially large number of arguments (one for each ivar to copy). The latter strikes me as especially ugly, but I suppose it doesn't need to be in the header and exposed to the world.</p>
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