# deduction guides for `std::valarray`

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< cpp‎ | numeric‎ | 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

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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