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POObjective-C Accessor Methods and Use of Autorelease
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  1. POObjective-C Accessor Methods and Use of Autorelease
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    copied!<p>I've been reading an apple document on Memory Management and am now a bit confused regarding the recommended implementation of Accessors. Apple cites 3 approaches in implementing accessors. </p> <p><strong>Technique 1</strong></p> <p>I've copied the code from the first technique which reflects: "Getter retains and autoreleases the value before returning it; setter releases the old value and retains (or copies) the new value." This first technique is stated to be more robust but suffers performance penalties on frequently called getters.</p> <pre><code>- (NSString*) title { return [[title retain] autorelease]; } - (void) setTitle: (NSString*) newTitle { if (title != newTitle) { [title release]; title = [newTitle retain]; // Or copy, depending on your needs. } } </code></pre> <p><em>skipping Technique 2</em></p> <p><strong>Technique 3</strong></p> <p>The third technique is better for frequently called setters and getters. This is also the method I've always followed.</p> <pre><code>- (NSString*) title { return title; } - (void) setTitle: (NSString*) newTitle { if (newTitle != title) { [title release]; title = [newTitle retain]; // Or copy, depending on your needs. } } </code></pre> <p><strong>My questions are:</strong></p> <ol> <li><p>(Technique 1) The setter first releases the existing value even if it doesn't point to anything. This would send a message to nil which I understand is supported in Objective-C but still looks odd. Am I understanding this correctly?</p></li> <li><p>(Technique 1) Why is the retain stacked inside an autorelease?</p></li> <li><p>(Technique 1) Is the caller whom uses the getter expected to call release after they're done with the object?</p></li> </ol> <p>The apple developer documentation page can be found at: <a href="http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmAccessorMethods.html" rel="nofollow">Memory Management Programming Guide - Accessor Methods</a></p>
 

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