Yeah, it can only be swapped out at link time (without crazy magic). That satisfies two very common cases though, when there is only one implementation (and the

Yeah, it can only be swapped out at link time (without crazy magic). That satisfies two very common cases though, when there is only one implementation (and the interface is a sacrifice to the OOP gods) and when the second implementation is for unit testing only. Those 2 plus other crazy rules (like only one interface defined per file) mean that many projects will end up with just as many interface files as a c++ project would header files.