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.