A semantics of the separation of interface and implementation in C++

C++ uses `class´ as the basis of `subtype polymorphism´ and `inheritance´, but it has been pointed out that the overloading of `class´ limits the expressiveness and makes its type system inflexible. This means that C++ and some other object oriented languages had to separate a class into two modules-an interface and an implementation. But, there seems to be no leading C++ model for separating the interface lattice from the implementation lattice. Moreover none of the proposed models describe the result of the separation in a formal way. As a result it is hard to understand what the type space would be like after the separation. The paper presents a formal model for the separation of interface and implementation in C++, and which explains the properties of the resulting type space after the separation