#include <stdio.h>
#include <assert.h>

void multiply_iio(multiply* self, double *a, double *b, double *p) {
  *p = *a * *b;
}

void multiply_oii(multiply* self, double *a, double *b, double *p) {
  *a = *p / *b;
}

// redundant
void multiply_ioi(multiply* self, double *a, double *b, double *p) {
  *b = *p / *a;
}

typedef enum { ignore, in, out, mode_t_n } mode_t; // TODO destructive input, update, pull?, ?? (where two args point to the same object)

typedef void (*proc3)(void *a, void *b, void *p);

typedef const proc3 proc3_modes[mode_t_n][mode_t_n][mode_t_n];

//typedef const proc3 proc3ary[2][2];

proc3_modes multiply_modes = {
  0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, multiply_iio, 0, multiply_ioi, 0,
  0, 0, 0, 0, multiply_oii, 0, 0, 0, 0
};

typedef struct {
  proc3_modes* modes;
} proc3_obj;

typedef struct {
  proc3_obj super;
} multiply;

void apply3(void* obj, mode_t aM, mode_t bM, mode_t cM, void *a, void *b, void *c) {
  proc3 func = (*(((proc3_obj*)obj)->modes))[aM][bM][cM];
  assert(func != 0);
  (*func)(obj, a, b, c);
}

int main() {
  double a, b, c;
  multiply m;
  m.super.modes = &multiply_modes;

  a = 7.0;
  c = 21.0;

  apply3(&m, in, out, in, &a, &b, &c);

  printf("%f %f %f\n", a, b, c);
}