// Define the gravity vector.
  b2Vec2 gravity(0.0f, -10.0f);

// Construct a world object, which will hold and simulate the rigid bodies.
b2World world(gravity);

// Define the ground body.
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0.0f, -10.0f);

// Call the body factory which allocates memory for the ground body
// from a pool and creates the ground box shape (also from a pool).
// The body is also added to the world.
b2Body* groundBody = world.CreateBody(&groundBodyDef);

// Define the ground box shape.
b2PolygonShape groundBox;

// The extents are the half-widths of the box.
groundBox.SetAsBox(50.0f, 10.0f);

// Add the ground fixture to the ground body.
groundBody->CreateFixture(&groundBox, 0.0f);

B2World world(0.0f, -10.0f);
B2Rect ground(0.0f, -10.0f, 100.0f, 20.0f);
world.add(&ground);

class Object{
void update();
void render();
void move();
void rotate();
}

class TriggerObject : Object{
void update(){ if in zone -> invoke(); }
}

world -> update(){
foreach object{
object.update();
object.render();
}
}

main{
World world;
world.add( new Object() );
world.add( new TriggerObject() );

loop{
world.update();
}
}

#define TRIGGER_OBJECT 1
#define OBJECT         0
typedef int type_object;

void trigger_update(trigger_object *);
void object_update(object *);

typedef struct {
      static const type_object type = TRIGGER_OBJECT;
      static const void (*update)(struct trigger_object *) = trigger_update;
} object;

typedef struct {
      static const type_object type = OBJECT;
      static const void (*update)(struct object *) = object_update;
} trigger_object;

...

int main()
{
      trigger_object t_obj;
      object obj;
      obj.update(obj);
      t_obj.update(t_obj);

      return 0;
}