[jonhohle]

You're right. I hadn't realized the compiler not only ensures the selector exists, but does type C-style type checking on dynamic calls as well. I was surprised to see that two messages with the same selector but different parameter types required a type cast to use.

Of course IMPs aren't identical if they take different parameters. This doesn't affect interchanging Objective-C types though. Yes, the arity and order are important, but the compiler doesn't enforce anything beyond that a pointer is passed for id types.

[nupark2]

Cheers to the peer comment regarding HN discourse. Unfortunately (?) I have more :)

> This doesn't affect interchanging Objective-C types though. Yes, the arity and order are important, but the compiler doesn't enforce anything beyond that a pointer is passed for id types.

This is true prior to ARC: all ObjC pointers are the same size, and hence ABI-compatible given equivalent arity/order. It's theoretically possible that a future ABI could be incompatible between two methods returning void vs pointer return value, but currently, all supported ABIs return pointer-sized values in a register.

However, with ARC, this changes. The type system has been effectively extended to denote the required referencing behavior for calling code. This means that for a given arity/order, you must also have equivalent referencing attributes.

[adriand]

I still find it disconcerting on HN when an argument ends with someone saying, "you're right". It's like the normal rules of the Internet just don't apply here. It's one of my favourite things about this community. To you, personally: kudos for maintaining that spirit!