Structural Typing is being used, but unlike the wikipedia article being linked to by mbell, I don't think the distinction between duck typing and structural typ

Structural Typing is being used, but unlike the wikipedia article being linked to by mbell, I don't think the distinction between duck typing and structural typing is that significant. It boils down to does the method parameter, which is an interface, describe the subset of the struct that you require or not? That is it. It is duck typing, but it simply requires explicit definitions (interfaces). To use a popular quote "if it acts like a duck-type it is a duck-type".