recompile after base class change

Question

In particular, the way most C++ implementations work implies that a change in the size of a base class requires a recompilation of all derived classes.

Answer 1

If it just the implementation, it should work fine. That's whole concept of Windows DLL's. Adding or removing interfaces won't changes the class size (unless you're introducing a new virtual function) but in the large extend the way functions laid out in the memory could be changed. So a recompilation is required if you're making use of the new function. On the other hand, most of the modern compilers are smart enough to identify the relevant changes because of a simple modification in the header files.