Re: Why is this casting needed?

[Helge Hess]

On Mar 24, 2006, at 21:17, Nate Smith wrote:
> Hello,
>
> I have two classes, A, and B, each which have "initWithNumber:" 
> methods.
> I have another class, C, which accepts an instantiated A object in one
> of its constructors. I compile the following 'code':
>
> C *c = [[C alloc] initWithA: [[A alloc] initWithNumber: 5]];
>
> The compiler gives me a warning saying that "initWithNumber:" has two
> definitions: one in A, and one in B. If I cast the result of [ A alloc 
> ]
> to (A*), no error is reported:
>
> C *c = [[C alloc] initWithA: [(A*)[ A alloc ] initWithNumber: 5]];
>
> Is this a bug or a feature? If GNUstep is using my regular GCC, my GCC
> version is 3.4.5.

This is a necessity, the compiler needs to know the type signature of 
the method to generate proper code. At least if it involves base types.

The return value of +alloc is 'id', so the compiler doesn't know the 
static class of the receiver of the 'initWithNumber:' method and 
therefore has two options. If you tell him using the cast, he can 
properly find the method declaration.

This is why you should avoid using the same selector with different 
signatures.

Greets,
  Helge
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