Alternative to polymorphism in non-OOP programming?

Question

Assume we have a drawing program with different elements, such as circle, rectangle, triangle and so on. Different kinds of objects that will all need similar function such as draw() to display themselves.

I wonder how would a programmer approach the problem that is nowadays typically solved by polymorphism, i.e. go through a collection of non-identical elements and invoke common functionality across the different objects.

One way that comes to mind is to have a struct with a function pointer to the appropriate function (or index in a function pointer array) as well as a void pointer to the actual instance, and pass the pointer which is cast to the proper type in the function. But that is just how I - a guy who is clueless on the subject would do it.

I do realize this might be a noobish question, but since I haven't been around in the "olden" days, I really wonder how was this problem tackled. What kind of approach was used in procedural programming and did it have a performance benefit, since we all do know polymorphism has an overhead even in fast languages like C++, due to the virtual method lookup.

Answer 1

A really simple example.

If this interest you you can find more of this in the Linux Kernel.

#include <stdio.h>                                                              

struct shape {                                                                  
    void (*say_hello)(void);                                                    
};                                                                              

void circle_say_hello(void)                                                     
{                                                                               
    printf("Hi I am circle!\n");                                                
}                                                                               

void square_say_hello(void)                                                     
{                                                                               
    printf("Meh I am square.\n");                                               
}                                                                               

#define ARRAY_SIZE(a) (sizeof(a)/sizeof(a[0]))                                  

int main(int argc, char *argv[])                                                
{                                                                               
    struct shape circle = { .say_hello = circle_say_hello, };                   
    struct shape square = { .say_hello = square_say_hello, };                   
    struct shape* shapes[] = {&circle, &square};                                
    int i;                                                                      

    for (i = 0; i < ARRAY_SIZE(shapes); i++) {                                  
        if (shapes[i] && shapes[i]->say_hello)                                  
            shapes[i]->say_hello();                                             
    }                                                                           

    return 0;                                                                   
}