CODEWITHSUNDEEP
objective-ccastingnsmutablearray
pasawaya
pasawaya

Reputation: 11595

Does Objective-C implicitly typecast NSMutableArrays to NSArrays when returned?

If I have a method like this:

-(NSArray *)methodThatReturnsAnArray;

And this is its implementation:

-(NSArray *)methodThatReturnsAnArray {

    NSMutableArray *aMutableArray = [[NSMutableArray alloc] init];
    [aMutableArray addObject:@"some string"];
    return aMutableArray;
}

Will Objective-C implicitly cast aMutableArray to NSArray when it is returned, or do I have to specify that like this:

    return (NSArray *)aMutableArray;

Upvotes: 1

Views: 398

Answers (4)

vikingosegundo
vikingosegundo

Reputation: 52227

A cast doesn't change an object's type. It just tells the compiler it should assume it is a object of an certain type. But a (NSArray *)aMutableArray will still be a NSMutableArray.

Upvotes: 0

Tom Dalling
Tom Dalling

Reputation: 24125

NSMutableArray is a subclass of NSArray, so yes, you don't have to do the type cast. It's textbook subtype polymorphism.

Upvotes: 3

Jack
Jack

Reputation: 133567

As with inheritance in object oriented languages in general, since NSMutableArray extends from NSArray class it IS A NSArray at all effect.

You don't need to cast it to a NSArray because it is already a NSArray, or in practice, it is able to respond to all messages to which an NSArray could respond so it can be used in replacement to it.

Upvotes: 2

DrummerB
DrummerB

Reputation: 40211

You can simply return the NSMutableArray object, since it's a subclass of NSArray.

Note that it will still be a mutable array however. Usually this isn't a problem, but if you want to make sure it's non mutable, you have to create a new instance or a copy.

return [NSArray arrayWithArray:aMutableArray];

Upvotes: 0

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