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    <p>While Carl is correct, that is almost assuredly exactly what you don't want to do.</p> <p>Namely, it is exceptionally rare in Cocoa or iOS to pass values by reference with the purpose of updating them remotely. Beyond being fragile and error prone, it is also generally a violation of encapsulation, a fundamental OO principal.</p> <p>Given context, it sounds like you are doing some kind of a baseball sort of app? Assuming so.</p> <p>Thus, you have a <code>Lineup</code> class whose instances represent a lineup within a Team (maybe even a Team class whose instances represent individual teams) with each team managing a lineup of <code>Player</code> instances.</p> <p>So, you might have something like:</p> <pre><code>@interface Lineup:NSObject - (BOOL) substitutePlayer: (Player *) sub; @end </code></pre> <p>And you might call it like this:</p> <pre><code>- (void)handleResult:(Result)result forPlayer:(Player *)player inLineup:(Lineup *)lineup { ... handle substituion ... [lineup substitutePlayer: player]; } </code></pre> <p>And you might implement the <code>substitutePlayer:</code> as:</p> <pre><code>- (BOOL) substitutePlayer: (Player *) playerToReplace; { NSUInteger *index = [self.players indexOfObject: playerToReplace]; [self.players replaceObjectAtIndex: index withObject: [self.substitutes objectAtIndex: 0]]; [self.substitues removeObjectAtIndex: 0]; return YES; } </code></pre> <p>By doing this, you avoid the goofy <code>(Player **)</code> stuff and you encapsulate all the lineup manipulation inside of the lineup class. If you were ever to need to specialize the lineup -- say, <code>-substitutePlayer:</code> should use the last guy in <code>self.substitutes</code> -- you could subclass <code>Lineup</code> and do so.</p> <p>End result; much cleaner OO design, much easier to maintain code, and much less fragile patterns.</p> <p>(Fixed some stupid bugs due to coding in SO's edit window.)</p>
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    1. COUpvote. In the last 6 or so years I don't think I've ever seen a "pass by reference for updating" in obj-c, except for NSError.
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    2. CO@kubi NSStream also comes to mind. There's probably a few others out there.
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      1. USCory Kilger
    3. COPass by reference is also used in Cocoa for multiple returns, with the "get" idiom: - (void)getLeftSprocket: (Sprocket **)outLeftSprocket andRightSprocket (Sprocket **)outRightSprocket withWidget: (Widget *)aWidget; Or, in an actual API: +[NSStream getStreamsToHost:port:inputStream:outputStream:]; (Return types for "get" methods vary from coder to coder. If nothing else, BOOL is pretty common because it's an immediate indicator of the success/failure of the message dispatch.)
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