method = func ptr with an implicit this-ptr

A Microsoft/TwoSigma developer revealed to me that basic OO features can be implemented in C with func ptr. A non-static method is
basically a C function whose first parameter is a ptr to the host object. The func's address is then saved as a func ptr field of
the struct. See also P342 [[headfirstC]]

I also read that in the early days of C++, every C++ source file was once converted to C source code and then compiled as C. That
means all c++ syntax features supported then were like sugar coating over C syntax, and some combination of C language features
(mostly pointers) could emulate all C++ features known then. This was the C++ early days. No longer possible.