Implementing Signatures for C++

We outline the design and detail the implementation of a language extension for abstracting types and for decoupling subtyping and inheritance in C++. This extension gives the user more of the flexibility of dynamic typing while retaining the efficiency and security of static typing. After a brief discussion of syntax and semantics of this language extension and examples of its use, we present and analyze the cost of three different implementation techniques: a preprocessor to a C++ compiler, an implementation in the front end of a C++ compiler, and a low-level implementation with back end support. Finally, we discuss the lessons we learned for future programming language design. 1 Introduction In C++, as in several other object-oriented languages, the class construct is used to define a type, to implement that type, and as the basis for inheritance, type abstraction, and subtype polymorphism. We argue that overloading the class construct limits the expressiveness of type abstraction,..