A Go type satisfies an interface by implementing the methods of that interface, nothing more. This property allows interfaces to be defined and used without -having to modify existing code. It enables a kind of "duck typing" that +having to modify existing code. It enables a kind of structural typing that promotes separation of concerns and improves code re-use, and makes it easier to build on patterns that emerge as the code develops. The semantics of interfaces is one of the main reasons for Go's nimble,