Настроение:	amused
Entry tags:	computing

Quikest way to implement C++ style OOP in C99
Sometimes it is useful to pack functions and related data into some single struct.
Yet without language support it can be a bit tedious.
Here is a set of macros to do that easier than in C++.
To implement a template class, just put your class code inside the header, and then

#define CLASS

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#define NOOP_IMPLEMENTATION
#include "noop.h"


#define CLASS CObj

METHODS
  void (*foo)(int a);
  int (*bar)(int a);
  CObj *(*set_xy)(int nx, int ny);

BDATA
  int x;
  int y;
EDATA

METH(void,foo,int a)
  printf("foo a=%d x=%d y=%d\n", a, this.x, this.y);
  printf("self.bar returned %d\n", self.bar(a+3));

METH(int,bar,int a)
  printf("bar a=%d x=%d y=%d\n", a, this.x, this.y);
  return a * 2;

METH(CObj*,set_xy,int nx, int ny)
  this.x = nx;
  this.y = ny;
  return &this;

CTOR
  o->x = 123;
  o->y = 456;

END


int main(int argc, char **argv) {
  CObj *a = new(CObj);
  CObj *b = new(CObj);
  $(a).set_xy(111,333);
  printf("a...\n");
  $(b).foo(69);
  printf("b...\n");
  $(a).foo(7);
  return 0;
}

#ifndef NOOP_H
#define NOOP_H
extern void *gthis_;

#define new(type) type##_init(malloc(sizeof(type)))

#define $(o) ((gthis_=(o)), *((o)->vtbl_))
#define self $(this_)
#define this (*this_)

#define PRFX_(prfx,mid,name) prfx##mid##name
#define PRFX(prfx,mid,name) PRFX_(prfx,mid,name)

#define METHODS typedef struct CLASS CLASS; typedef struct {

#define BDATA } PRFX(CLASS,_,CVtbl); struct CLASS {CObj_CVtbl *vtbl_;
#define EDATA }; PRFX(CLASS,_,CVtbl) PRFX(CLASS,_,vtbl_); \
  void PRFX(CLASS,_,dummy_)() {

#define METH(type, name, ...) } \
  type PRFX(CLASS,_,name) (__VA_ARGS__); \
  __attribute__((constructor)) void PRFX(CLASS,__init__,name)() { \
    printf("initing %s\n", #name); \
    PRFX(CLASS,_,vtbl_).name = &PRFX(CLASS,_,name); \
  } \
  type PRFX(CLASS,_,name) (__VA_ARGS__) { CLASS *this_ = gthis_;


#define MINIT(name) PRFX(CLASS,_,vtbl_).name = PRFX(CLASS,_,name)
#define CTOR } CLASS *PRFX(CLASS,_,init)(CLASS *o) \
  { o->vtbl_ = &PRFX(CLASS,_,vtbl_);

#define END }




#ifdef NOOP_IMPLEMENTATION
void *gthis_;
#endif

#endif