NSExpression contains a built-in function for calculating the distance between two CLLocation instances. Using it is straightforward:

The result will be an instance of NSNumber with the distance between the two locations. The arguments can be constant values, key paths, etc.

Because NSPredicate is really a tree of expression operations we can use it there too:

Filtering and searching collections of CLLocation objects by distances becomes fast and easy - there is no reason to implement your own distance methods.