I was working on a C code base with classes, inheritance, and polymorphism, all done by hands and macros.

Something like

typedef struct s_some_class {
    void (*method)(this *s_some_class);
} t_some_class;

Overall, learning C was the best enabler in my whole career. For instance I was learning Python by tinkering with CPython VM, so when I see these ‘WAT’ quircks I know exactly what’s up.