Swift Programming: The Big Nerd Ranch Guide

Naming Things: A Cautionary Tale

There is an edge case with protocol extensions that may prove to be a great source of frustration if you are not careful. In the previous section, you added description to the requirements of ExerciseType, added a default implementation, and added a specific implementation to Treadmill that took precedence over the default implementation. This worked correctly because description was required by the ExerciseType protocol. What happens, though, if you write a protocol extension to add a property or method, then add the same property or method (with a different implementation) to a conforming type?

The answer is that it depends on how the instance is being accessed – does the compiler know its specific ...