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deduction guides for std::array

Defined in header <array> 
template< class T, class... U >
array( T, U... )
  -> array<T, 1 + sizeof...(U)>;
 (since C++17)

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 <array>
#include <cassert>
 
int main()
{
    int const 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 alternative,
                                                   // creates std::array<short, 3>
}

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