Why is there no way to do introspection in Objective C with Objects?

Question

I have seen examples (on here especially) of calling hideous C functions and getting structures back that have to be iterated, replete with reams of underbars.

Why can't I do this (pseudo to follow):

  Money *cost = [[Money alloc] init];

  for (Property *property in [[cost class] properties]){
    ..
  }

  for (Method *method in [[cost class] methods]){
    ..
  }

?

Answer 1

Those functions are not hideous. They are all documented in the Objective-C Runtime Reference.

One reason I think there aren't the +properties and +methods methods are because it's rare you need to look for property/method that you don't know the name in compile time.

The most useful introspection functions in ObjC are -respondsToSelector:, -isKindOfClass:, -conformsToProtocol:, NSInvocation, KVC, KVO, NSXxxxFromString, and they are operating with objects.

Answer 2

Here's why you can't do it: Because Cocoa operates on a level above the runtime. The Objective-C runtime functions can't reasonably depend on Cocoa, an optional library implemented on top of it. It would be possible to create an object-oriented layer on top of the runtime API, but this was not a design goal of Cocoa. It's just not necessary to do what Cocoa does.

Answer 3

Check out NSClassDescription and the cover methods on NSObject. This may be close to what you are looking for.