deduction guides for std::array

One deduction guide is provided for std::array to provide an equivalent of std::experimental::make_array for construction of std::array from a variadic parameter pack .

The program is ill-formed if ( std:: is_same_v < T, U > && ... ) is not true. Note that ( std:: is_same_v < T, U > && ... ) is true when sizeof... ( U ) is zero.

Example

#include <algorithm>
#include <array>
#include <cassert>
#include <type_traits>
int main()
{
    const int x = 10;
    std::array a{1, 2, 3, 5, x}; // OK, creates std::array<int, 5>
    assert(a.back() == x);
//  std::array b{1, 2u}; // Error, all arguments must have the same type
//  std::array<short> c{3, 2, 1}; // Error, wrong number of template args
    std::array c{std::to_array<short>({3, 2, 1})}; // C++20 facility
    assert(std::ranges::equal(c, std::array{3, 2, 1}));
    static_assert(std::is_same_v<short, decltype(c)::value_type>);
}