a sub-class to have more than one base class. We distinguish between base classes that are pure interfaces and those that have an implementation. Multiple implementation inheritance may let you re-use first one, are pure interfaces. In order to ensure that they remain pure interfaces, they must end with the Interface suffix. There is an exception to this rule on Windows. Interfaces Classes that satisfy compile-time computation in the type domain. Template metaprogramming allows extremely flexible interfaces that are type safe and high performance. Facilities like Google Test, std::tuple, std::function