deduction guides for std::valarray

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std::valarray
Member functions
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Deduction guides (C++17)
Defined in header <valarray>
template < typename T, std:: size_t cnt >
valarray ( const T ( & ) [ cnt ] , std:: size_t ) - > valarray < T > ;
(since C++17)

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).

Example

Run this code 
#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';
}

Output: 

1 2 3
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