> Riccardo Mottola wrote: >> if ([cs isKindOfClass:[NSCharacterSet class]]) >> NSLog(@"is NSCharacterSet"); >> if ([cs isKindOfClass:[NSMutableCharacterSet class]]) >> NSLog(@"is NSMutableCharacterSet"); > > if this is a safe test - and it ought to be - then it passes also on > venerable 10.4. So actually it is there that the Xcode doc. lies, since it > returns a NSMutableCharacterSet.
Sorry, but no. Xcode doesn't "lie" here. First of all, it's the essence of subtyping polymorphism in OO languages that you are free to return an object of any subclass of the method's declared return type. Since any NSMutableCharacterSet is also a NSCharacterSet, there is nothing wrong with returning a mutable character set when the method's return type is NSCharacterSet. The documentation also nowhere claims that any of these methods returns an object that is an instance of the class NSCharacterSet. (The old OpenStep documentation even explicitly says that these methods return an instance of some private subclass of NSCharacterSet.) But anyway, the different return types do make sense here, since Apple's Foundation framework does remember whether you've requested a mutable or an immutable character set. Just try and cheat pretending the methods do actually return a mutable character set, e.g., [(NSMutableCharacterSet *)[NSCharacterSet decimalDigitCharacterSet] addCharactersInString: @"abcdef"]; and see what happens. :-) Wolfgang
