Question

Atm i have sth like that:

template<int n>
struct Pow
{
  enum{val= Pow<n-1>::val<<1};
};
template<>
struct Pow<0>{
    enum{val =1};
};

I can acess data like Pow<30>::val. It’s good but i want do like this

   int main()
    {
    Pow<30>::val;

and then use variable to
access all of value <0,30>
I knew that i can use array and dynamic programming but can i do that in this way?
Sorry for English.

Answer 1

Using C++0x variadic templates:

template<int... Indices>
struct powers {
    static const int value[sizeof...(Indices)];

    typedef powers<Indices..., sizeof...(Indices)> next;
};

template<int... Indices>
const int powers<Indices...>::value[sizeof...(Indices)] = { Pow<Indices>::val... };

template<int N>
struct build_powers {
    typedef typename build_powers<N - 1>::type::next type;
};

template<>
struct build_powers<1> {
    typedef powers<0> type;
};

and then:

int
main()
{
    // we want [0..30] inclusive so pass 31 as exclusive upper limit
    typedef build_powers<31>::type power_type;
    // 0..30 is 31 powers in all
    typedef const int array_type[31];

    array_type& ref = power_type::value;
    // ref[0] .. ref[30] are the values of Pow<0>::val .. Pow<30>::val
}

So that’s with using an array but without dynamic initialization. Since you want the result as a variable and not for TMP I feel this is adequate.