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deduction guides for std::optional

From cppreference.net
C++
Utilities library
std::optional
Defined in header <optional>
template < class T >
optional ( T ) - > optional < T > ;
(since C++17)

One deduction guide is provided for std::optional to account for the edge cases missed by the implicit deduction guides, in particular, non-copyable arguments and array to pointer conversion.

Example

Run this code 
#include <optional>
#include <type_traits>
int main()
{
    int a[2];
    std::optional oa{a}; // uses explicit deduction guide
    static_assert(std::is_same_v<decltype(oa), std::optional<int*>> == true);
}