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POPolymorphic variable in Objective-C
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copied!<p>Let's say I have a class named <code>Parent</code> and two derived classes called <code>Child1</code> and <code>Child2</code>.</p> <pre><code>@interface Parent : NSObject { NSString *fooVariable; -(void)foo; } @end @interface Child1 : Parent { -(void)bar1; } @end @interface Child2 : Parent { -(void)bar2; } @end </code></pre> <p>Now imagine I have a method called <code>foo</code> and in some cases I want to pass it as a parameter an instance of <code>Child1</code> and in some other cases an instance of <code>Child2</code>. Depending on the class type I want to call either method <code>bar1</code> or <code>bar2</code>.</p> <p>How can I achieve this in Objective-c? </p> <p><strong>What I've tried:</strong></p> <p>I decided to use the following signature and implementation:</p> <pre><code>-(void)fooWithObject:(Parent *)instance{ if ([instance isKindOfClass:[Child1 class]]){ [instance bar1]; } else{ [instance bar2]; } } </code></pre> <p>So now I can do this:</p> <pre><code>Parent *instance = [[Child1 alloc] init]; //This call is supposed to lead to an invocation of bar1 inside the foo method [self fooWithObject:instance] instance = [[Child2 alloc] init]; //This call is supposed to lead to an invocation of bar2 inside the foo method [self fooWithObject:instance] </code></pre> <p>Unfortunately, when I try to compile my code the compiler complains that there's is no method bar1 (or bar2) declared in my Parent's interface. </p> <p>According to a some tutorials online you can do the following, so theoretically my approach should work:</p> <pre><code>NSArray *anotherArray = [NSMutableArray array]; // This mutable-only method call is valid but // produces a compile-time warning [anotherArray addObject:@"Hello World"]; </code></pre>

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