ARC - why do object pointers require explicit ownership type in function definitions?

Question

void testFunction (id testArgument[]) {
    return;
}

I'm getting the error "Must explicitly describe intended ownership of an object array parameter". Why does ARC need me to specify the ownership type of the objects in the testArgument array?

Answer 1

To expand on Jeremy's answer, ARC had two primary goals when designed:

• make memory management as fully automatic as possible in pure Objective-C code while also preserving or maximizing efficiency (in fact, ARC can be more efficient than manual retain release).

• require exactly specific declaration of memory management intent when crossing the boundary between C and Objective-C.

As well, the implementation of ARC is extremely conservative. That is, anywhere where the behavior has traditionally been "undefined", ARC will spew a warning.

Thus, in this case, the declaration of intent is required so that the compiler can apply a consistent and specific set of memory management rules to the contents of the array.

Answer 2

Because ARC needs to know whether to insert retain/release calls for you to avoid memory leaks.