Question

Say class A depends on Class B and via versa.

So obviously in a.h I would put #import”b.h” and in “b.h” I would import “a.h”

After that

Should we

declare @class A

in b.h AND @class B in a.h

Should we do both or should we use @class only once?

Why?

I reasoned that if I do it only once, say including @class B in a.h, given that a.h also contains #import “b.h” then the class a.h already knows about b.h

However it seems that I got to do it both in xcode and I wonder why.

Answer 1

There’s nothing wrong with using a forward declaration (i.e. @class Foo) in the header file for each class. You can do that if all you need is for each class to reference the other. A forward declaration just tells the compiler “This name refers to a class, and the actual declaration of the class will come later.”

As you say, you could also use a forward declaration of B in A.h, and then just import A.h in B.h. I don’t think there’s any real benefit to doing that unless there are other things in A.h that you also need to reference in B.h.

However it seems that I got to do it
both in xcode and I wonder why.

If you mean that you’re getting an error when you import A.h in B.h instead of using a forward declaration of A, please post the error. I don’t think there should be a problem with that. (And in any case, the issue would be a compiler issue or an Objective-C issue, not an Xcode problem. Xcode is just the IDE.)