Variable number of constructor parameters depending on integer template

Question

I\'m writing a container storage class template that wraps a private std::array in order to add some functionality to it. The template parametrises the number o

Answer 1

By following Member function template with the number of parameters depending on an integral template parameter and Variadic templates with exactly n parameters, have got it working with the following code.

template<size_t N> class Vector {
private:
    array<double, N> vals;
public:
    template <typename ...T,
          typename enable_if<sizeof...(T) == N, int>::type = 0>
    Vector(T ...args) : vals{args} {}
};

Answer 2

Don't get what you mean by this:

Variadic arguments don't provide a mechanism to check how many of them there are, so they're right out

template <typename ...T>
Vector(T... args) {
    static_assert(sizeof...(args) <= N, "oops");
}

Should work..

Answer 3

You could additionally generate a pack of the right size via some template specialization tricks:

template <size_t N, class = std::make_index_sequence<N>>
class Vector;

template <size_t N, size_t... Is>
class Vector<N, std::index_sequence<Is...>> 
{
private:
    std::array<double, N> vals;

    template <size_t >
    using double_ = double;
public:
    Vector(double_<Is>... vals)
    {
        ...
    }
};

That is a non-template constructor which takes N doubles.