May I use a constant number to choose a class at compile time, possibly using templates?

Question

Let\'s say I have a constant value (possibly of some enum type). Let\'s say I have many classes A, B, D, etc.

Can I have something like this?

C<1>          


        

Answer 1

This isn't the only way to do this, but I hope acceptable for your purposes:

struct A { };
struct B { };

template 
struct choices;

template <>
struct choices<1> { typedef A type; };

template <>
struct choices<2> { typedef B type; };

template 
using C = typename choices::type;

---

Update: To do the same without C++11 features, you should make C a class with a typedef member type equal to the corresponding type alias above:

template 
struct C
{
    typedef typename choices::type type;
};

// ...
C<1>::type anInstanceOfA;
C<2>::type anInstanceOfB