> What is the size of A? Answer: you never know in C++ due to polymorphism. It might be a B or other subclass. It is truly a variable length operation.

You could easily go around it.

The compiler knows when creating the destructor for B.

In your example, to have correct C++, you need to have declared a virtual destruct-or for B. You could encode the size of B in a static offset from the virtual destructor or simply as a return value from it.

This is not how it is done now, mainly because how free was designed in C.

free() design is a terrible mistake. Probably one of the worst design mistake of C with the null terminated / no-length specified string and the preprocessor.