Question

For my game,

Everything inherits from Entity, then other things like Player, PhysicsObject, etc, inherit from Entity. The physics engine sends collision callbacks which has an Entity* to the B that A collided on. Then, lets say A is a Bullet, A tries to cast the entity as a player, if it succeeds, it reduces the player’s health.

Is this a good design?

Thanks

Answer 1

I believe that messaging system is somehow better suits your “world”.

Entity* target = ...;
bool    handled = target->send(M_COLLIDE, ...);

In this case you will not need neither dynamic casts nor to check result of dynamic cast.

Update, here is an example:

target->send(M_COLLECT, pMushroom);
...

Person::handle(uint message, Entity* the_thing)
{
  switch(message) 
  {
    case M_COLLECT: this->things.push( the_thing ); 
                    the_thing->send(M_COLLECTED_BY, this); break;
  }
}

Entity::handle(uint message, Entity* the_thing) implementation can be wrapped into
MSG_MAP_START, MSG_MAP_END and HANDLE_MSG(msg) macros so your code will look like:

MSG_MAP_START

   HANDLE_MSG(M_COLLECT)
   {
     this->things.push( the_thing ); 
     the_thing->send(M_COLLECTED_BY, this);
   }
   HANDLE_MSG(M_COLLECTED_BY) 
   {
     ...
   }
   ...
MSG_MAP_END

Many variations of this are possible.

By the way Objective-C has this kind of messaging built-in into the language. With extremely ugly notation but still.