Can I get "macro polymorphism" in C - c

Question

The type of polymorphism I'm after is this:
suppose I have a macro called draw(), and I have 2 structs, one called circle and the other called square. Is is possible to somehow do something like this:
#define draw() // can I get the text that's behind the macro?
//then maybe, with _Generic achieve this?
void draw_circle(struct circle);
void draw_square(struct square);
struct circle c;
struct square s;
c.draw();//draw is a macro. this time it is supposed to expand to draw_circle(c);
s.draw();//supposed to expand to draw_square(s);
EDIT_1: this is what I have so far, after reading your answers.
//raw_array.h
#pragma once
#include <stdint.h>
#include <stdlib.h>
#define byte uint8_t
#define _GET_OVERRIDE(_1, _2, _3, NAME, ...) NAME
/*#define init_impl(...) _GET_OVERRIDE(__VA_ARGS__, \
init_impl3, init_impl2, init_impl1)(__VA_ARGS__)
#define init( name, ... ) (raw_array * (name); init_impl( (name), __VA_ARGS__))*/
#define array_init_impl(...) _GET_OVERRIDE(__VA_ARGS__, init_array_impl3, init_array_impl2, init_array_impl1)(__VA_ARGS__)
///<summary>creates a variable of type raw_array with name as an identifier, and initializes based on the parameters</summary>
#define RAW_ARRAY( name, ... ) raw_array (name); array_init_impl( (&name), __VA_ARGS__)
typedef struct indexable_memory_block_struct
{
raw_array * _self;
byte * bytes;
size_t element_size;
size_t number_of_elements;
} raw_array;
///<summary>starts the an empty raw_array. only element_size is set.</summary>
///<param name=r_arr>the raw_array to be initialized</param>
///<param name=element_size>the size of the elements in this raw_array</param>
void init_impl1 ( raw_array * r_arr, size_t element_size )
{
r_arr = malloc ( sizeof ( raw_array ) );
r_arr->element_size = element_size;
r_arr->number_of_elements = 0;
r_arr->bytes = NULL;
r_arr->_self = r_arr;
}
///<summary>
///starts the raw_array an empty. byte with its bytes allocated
///to their default value (0).
///</summary>
///<param name=r_arr>the raw_array to be initialized</param>
///<param name=element_size>the size of the elements in this raw_array</param>
///<param name=number_of_elements>the number of elements in the array</param>
void init_impl2 ( raw_array * r_arr, size_t element_size, size_t number_of_elements )
{
r_arr = malloc ( sizeof ( raw_array ) );
r_arr->element_size = element_size;
r_arr->number_of_elements = number_of_elements;
r_arr->bytes = calloc ( number_of_elements, element_size );
r_arr->_self = r_arr;
}
///<summary>
///starts the raw_array copying its contents from a normal array.
///</summary>
///<param name=r_arr>the raw_array to be initialized</param>
///<param name=arr>the normal C array whose contents will be copied to this raw_array</param>
///<param name=element_size>the size of the elements in this raw_array</param>
///<param name=number_of_elements>the number of elements in the array</param>
void init_impl3 ( raw_array * r_arr, const void * const arr, size_t size_of_element, size_t number_of_elements )
{
r_arr->bytes = malloc ( size_of_element * number_of_elements );
memcpy ( r_arr->bytes, arr, size_of_element * number_of_elements );
r_arr->element_size = size_of_element;
r_arr->number_of_elements = number_of_elements;
r_arr->_self = r_arr;
}
there are other parts, but these are the ones currently being ported to this new syntax. Now main:
int main ( int argc, char * argv[] )
{
int data[30];
//line bellow has a compilation error: *expected a ')'*
init ( r_arr, data, sizeof ( int ), 30 );
}
what does it mean expected a ')'
could you guys check out the macro syntax?
About _Generic, I learned about it today, and I'll use it if it's useful, for sure.
EDIT_2: found a gross error, will be fixing it and editing again. Visual Studio is updating (12GB...) So I can't build anything at the moment. [mini-edit]: Guess I fixed the gross error at least. [mini-edit] another very bizarre error in my code, I stringifyed the name token, wth?! corrected now.
EDIT_3: having slept and having VS operational again, I fixed the macros, will edit them and comment out the wrong code. Now I need to the circle.draw() behaviour... any ideas?

Answer 1

Besides #LirooPierre s approach, you could also use C11 Generics. Yes you heard right, C has generics now.
Consider this example:
#include <stdio.h>
#define draw(X) _Generic((X), \
struct circle: draw_circle, \
struct square: draw_square \
)(X)
struct circle{};
struct square{};
void draw_circle(struct circle a)
{
printf("Drawing a circle\n");
}
void draw_square(struct square a)
{
printf("Drawing a square\n");
}
int main(void)
{
struct square a;
draw(a); // "Drawing a square"
}
But even though it should be portable, it sadly is not. M$ Compiler doesn't implement them, but clang and gcc do.

Answer 2

You can really only achieve what want in c with function pointers
struct shape {
{
void (*draw)(struct shape);
};
void draw_circle(struct shape);
void draw_square(struct shape);
#define CIRCLE(c) struct shape c; c.draw = &draw_circle;
#define SQUARE(s) struct shape s; s.draw = &draw_square;
Now you can do something like this:
CIRCLE(c)
SQUARE(s)
c.draw(c);
s.draw(s);
You could add a draw macro too if you don't like the c.draw(c) syntax.
#define DRAW(shape) shape.draw(shape)
DRAW(c);
DRAW(s);

Answer 3

Yes it is possible !
You have to create a pointer on a function in your struct like this:
typedef void (*t_draw)(struct circle); //create a new type called t_draw
struct circle {
t_draw draw;
}
Now in your code you have to assign a function in your struct:
struct circle c;
c.draw = &draw_circle;
and call it by using:
c.draw(/*your args*/);
Create the second structure square like the first and it should be OK !