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    <p>I don't know what is in the CDP that Steve referenced but basically the Objective-C Class Cluster is a construct that supports implementing the abstract <a href="http://en.wikipedia.org/wiki/Factory_method_pattern" rel="noreferrer">Factory</a> pattern.</p> <p><strong>The <em>idea</em> is simple</strong>: You want to provide a Factory (Cluster) interface that, with minimal description, manufactures and returns a specific concrete instance of a Factory Object that satisfies the behavior of the cluster family described by the Factory (Cluster) interface.</p> <p><strong>A simple concrete example</strong>: This example provides a Laugh factory that produces concrete classes of specific laughter types (e.g. Guffaw, Giggle). Pay attention to the <em>Laugh initWithLaughter:</em> method.</p> <p>In Laugh.h:</p> <pre><code>#define kLaughWithGuffaw 1 #define kLaughWithGiggle 2 @interface Laugh: NSObject {} - (Laugh *) initWithLaughter:(NSUInteger) laughterType; - (void) laugh; @end </code></pre> <p>In Laugh.m:</p> <pre><code>@interface Guffaws:Laugh {} - (void) laugh; @end @interface Giggles:Laugh {} - (void) laugh; @end @implementation Laugh - (Laugh *) initWithLaughter:(NSUInteger) laugherType { id instanceReturn=nil; ; // Removed for ARC [self release] if ( laughterType == kLaughWithGuffaw ) instanceReturn = [[Guffaws alloc]init]; else if( laughterType == kLaughWithGiggle ) instanceReturn = [[Giggles alloc]init]; else ; // deal with this return instanceReturn; } - (void) laugh { NSLog(@"Humbug"); } @end @implementation Guffaws - (void) laugh { NSLog(@"OH HA HA HOWAH HA HA HA"); } @end @implementation Giggles - (void) laugh { NSLog(@"Tee hee"); } @end </code></pre>
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    1. POWhat exactly is a so called "Class Cluster" in Objective-C?
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    1. USFrank C.
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    1. COWhile the other answers were good providing doc & book links, I like this because it makes it nice and simple to see how to actually do this. Thanks
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      1. USjamone
    2. CO+1 for small example !!
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      1. USTheTiger
    3. CO+1 for the nice and effective explanation...!!!! keep it up.....
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      1. USKamarshad
 

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