Re: Garbage collector vs variable lifetime

FROM : Charles Srstka
DATE : Tue Jun 10 17:28:13 2008

On Jun 9, 2008, at 5:55 PM, Hamish Allan wrote:

> Sure. But it gives you *more* information than if it just returns
> "id". I agree with you in all other respects of your post, but I don't
> agree that +[NSArray array] returns "id" because if it returned
> "NSArray *" you'd have to have a separate declaration for
> +[NSMutableArray array]. Indeed, that line of reasoning leads to
> John's way of thinking: that if you return something more specific
> than "id", it is in some sense indicative that the returned object is
> more likely to be of a specific class, rather than a subclass thereof.


I think the problem is that if NSArray has +[NSArray array] returning 
an NSArray, then NSMutableArray has to return an NSArray also, since 
it can't have a different method signature for the same method. As a 
result, if you called +[NSMutableArray array], the compiler would 
think you were getting a regular, non-mutable NSArray, and you'd get a 
warning if you tried to do this, although the code would still work:

NSMutableArray *array = [NSMutableArray array];

The only way to get the compiler warnings to shut up would be to cast 
it. If the methods return id, then the compiler just assumes you're 
doing the right thing (which also means you can do stupid things like 
assign +[NSMutableArray array] to an NSString or something which would 
of course end up blowing up before too long, so it's not perfect 
either, but it's certainly less annoying than having to typecast every 
assignment of a newly-initialized NSMutableArray).

Charles