deduction guides for std::optional

template<class T>
optional(T) -> optional<T>;

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

#include <optional>
 
int main()
{
    int a[2];
    std::optional oa{a}; // explicit deduction guide is used in this case
}