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deduction guides for std::valarray

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

#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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