deduction guides for std::valarray

Since C++17

Header: <valarray>

This deduction guide is provided for std::valarray to allow deduction from array and size (note that deduction from pointer and size is covered by the implicit guides).

# Declarations

template< typename T, std::size_t cnt >
valarray( const T(&)[cnt], std::size_t ) -> valarray<T>;

(since C++17)

# Example

#include <iostream>
#include <valarray>
 
int main()
{
    int a[] = {1, 2, 3, 4};
    std::valarray va(a, 3); // uses explicit deduction guide
    for (int x : va)
        std::cout << x << ' ';
    std::cout << '\n';
}