class Entity {
public:
    virtual ~Entity() { }

    virtual void Touch( Entity *e )
    {
    }
};

class Player : public Entity
{
public:
    //....
};

class Item : public Entity {
public:
    virtual void Touch( Entity *e )
    {
        if( e->type == Player::type )
        {
            //...
        }
    }
};