Question

I’ve got an entity class, a base component class and a few base component derived ones. The entity class contains an array of base component pointers:

class CComponent
{
public:
  static unsigned GetType() { return -1; }; //Base identifier 
  //...
};

---

class CPoint : CComponent
{
  public:
    static unsigned GetType() { return 0; }; //Point identifier 
}

---

class CEntity
{
private:
  CComponent* aComponents[3];
public:
  // ... 
  //Getter by component ID here!
};

---

I would like to know how can I map a specific component type along with its integer identifier (for the CPoint component class, it would be 0) so I can easily cast it to the right type, in my Entity class.

Example: Suppose I’ve added a CPoint component to the entity component array (in position 0 of course), and I want to retrieve it as a CPoint (type-casting) by inputting the component integer identifier (in this case, 0). I want to avoid huge ‘switch’ cases as much as possible!

PS: I don’t want to use loads of virtual functions in my base component class that match with properties in my derived ones. (I don’t want to have a virtual SetPos function in my base component class, while it’s place is in the CPoint class);

PS#2: As commented by ‘etarion’, I would like something like this:

dynamic_cast<get_type_for(0)*>(obj)

Of course, that’s the mechanism I want to achieve, I don’t know if it’s possible or not.

Answer 1

Well I know of some ways to achieve the sort of thing you want :

• with gcc you can use the non standard typeof(some_type) function which gives you the type to dynamically cast your type. See here.
• with C++0x there is a standard way that mimics typeof : decltype(some_type)
• you can use the standard typeid that gives you a type_info class which implements operator==
• boost::variant is another way mentioned in one of the comment (I do know it well …)

my2c