> reimplement it's interface Implicitly assumes we know what that interface is (and this assumes that that "interface" really does include all the relevant int

> reimplement it's interface Implicitly assumes we know what that interface is (and this assumes that that "interface" really does include all the relevant interactions - this is, the literal interface between systems). If we really did know this true interface, the implementation is absolutely irrelevant. In practice, all abstractions are leaky, and it's routinely simpler to look at the source to work out what it does. This covers the gamut of interactions, from minor undocumented API details, to complex semamtocs of corner cases, to time/space/resource usage patterns.