Question

What is NSComparisonResult and NSComparator?

I’ve seen one of the type definitions, something like that:

typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);

Is it any different from a function pointer?

Also, I can’t even guess what the ^ symbol means.

Answer 1

^ signifies a block type, similar in concept to a function pointer.

typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);
//          ^                      ^                ^
//   return type of block      type name       arguments

This means that the type NSComparator is a block that takes in two objects of type id called obj1 and obj2, and returns an NSComparisonResult.

Specifically NSComparator is defined in the Foundation Data Types reference.

And to learn more about C blocks, check out this ADC article Blocks Programming Topics.

Example:

NSComparator compareStuff = ^(id obj1, id obj2) {
   return NSOrderedSame;
};

NSComparisonResult compResult = compareStuff(someObject, someOtherObject);