Variadic native functions

[nikomatsakis]

We should support variadic native functions like objc_msgSend() or printf().

[catamorphism]

Nominating for "maturity #3 - feature complete"

[emberian]

Triage bump

[catamorphism]

Low, not 1.0

[lilyball]

For the record, objc_msgSend() is not a variadic function. It's a hand-coded assembly trampoline that finds the real function and calls it. The real function uses normal C calling conventions, not varargs conventions (unless, of course, it actually includes varargs itself).

When using objc_msgSend() directly in code, you must cast it to the appropriate type. For example, in order to call a theoretical method -[NSObject setInteger:(int)i] you need to say

((void(*)(id,SEL,int))objc_msgSend)(obj, @selector(setInteger:), i);