Objective-C Protocol Madness — how to return object based on protocol?

Question

@protocol Eating
@end

@interface Eat : NSObject<Eating>
{
}
- (id<Eating> *)me;
@end

@implementation Eat
- (id<Eating> *)me { return self; }
@end

In the above piece of Objective-C code, why does "return self" result in a "Return from incompatible pointer type" warning? What's the incompatible pointer type and how to fix it?

Answer 1

Because id is a pointer itself, you don't need the asterisk.

@interface Eat : NSObject<Eating> {
}
- (id<Eating>)me;
@end

Answer 2

好的..答案是“id”而不是“id *”。

Answer 3

remove id * and replace with id. id is already a pointer.

Answer 4

Because id is essentially NSObject * (although there are some minor differences). Thus, when you return self , you are returning -(NSObject *) . What you have is id * which is like NSObject ** .

Answer 5

You are slightly off in your use - it's:

- (id<Eating>)me { return self; }

(because you are returning id, not a pointer to an object).