/*
** $Id: oldobj.c 802 2008-03-01 19:26:43Z phf $
**
** A simple way to fake objects through structs and
** function pointers. Very few people use stuff like
** this, except maybe to define certain interfaces
** for others to "plug into". See the spam filter
** code you read early in the semester and the way
** its database interface was set up. :-)
**
** Sorry, no comments, but you can look stuff like
** this up online. Here are a few pointers:
**
**   http://www.cs.usfca.edu/~parrt/course/652/lectures/polymorphism.html
**   http://onestepback.org/articles/poly/
**   http://www.d.umn.edu/~gshute/softeng/ooC/ooC.html
**
** And let's not forget the magnum opus of this kind
** of hacking:
**
**   http://ldeniau.web.cern.ch/ldeniau/html/oopc.html
**
** We'll just switch to C++ instead, but it's nice to
** know how the basic OO stuff works under the hood...
*/

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

typedef struct rectangle* Rectangle;

struct rectangle {
  int width;
  int height;
  int (*area)( Rectangle );
};

int rectangle_area( Rectangle this )
{
  return this->width * this->height;
}

Rectangle make_rectangle( int width, int height )
{
  Rectangle new = malloc( sizeof( struct rectangle ) );
  new->width = width;
  new->height = height;
  new->area = rectangle_area;
  return new;
}

int insane_area( Rectangle this )
{
  return this->width * this->height * 4 - 27;
}

Rectangle make_insane( int width, int height )
{
  Rectangle new = malloc( sizeof( struct rectangle ) );
  new->width = width;
  new->height = height;
  new->area = insane_area;
  return new;
}

int area( Rectangle r )
{
  return (*r->area)(r); // "polymorphic" call!
}

int main( void )
{
//  Rectangle r = new Rectangle(10,20);
  Rectangle r = make_rectangle( 10, 20 );
  Rectangle q = make_insane( 10, 20 );
  printf( "%d\n", r->width);
//  printf( "%d\n", r.area() );
  printf( "%d\n", (*r->area)(r) );
  printf( "%d\n", (*q->area)(q) );
  printf( "%d\n", area(r) );
  printf( "%d\n", area(q) );
  return EXIT_SUCCESS;
}