Global and Local Virtual Functions in C++

Global virtual functions (GVFs) are introduced as C++ functions defined at global or namespace scope which can be redefined later similar to virtual member functions. Even though GVFs are a relatively simple concept, hardly more complex than ordinary C functions, it is shown that they subsume object-oriented single, multiple, and predicate-based method dispatch as well as aspect-oriented before, after, and around advice. Furthermore, the well-known “expression problem ” can be solved in a simple and natural way. Local virtual functions are a straightforward extension of GVFs allowing temporary redefinitions during the execution of some other function or part of it. Amongst others, this is quite useful to simulate “cflow join points ” of aspect-oriented languages. The implementation of global and local virtual functions by means of a precompiler for C++ is briefly described.