Object-orientation in C

Question

What would be a set of nifty preprocessor hacks (ANSI C89/ISO C90 compatible) which enable some kind of ugly (but usable) object-orientation in C?

I am familiar with

Answer 1

If I were going to write OOP in C I would probably go with a pseudo-Pimpl design. Instead of passing pointers to structs, you end up passing pointers to pointers to structs. This makes the content opaque and facilitates polymorphism and inheritance.

The real problem with OOP in C is what happens when variables exit scope. There are no compiler-generated destructors and that can cause issues. Macros can possibly help, but it is always going to be ugly to look at.