# 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 <valarray>
    int main() {
      int a[] = {1, 2, 3};
      std::valarray va(a, 3); // uses explicit deduction guide
    }

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