is_constructible_v<T, const U&> is true,
is_assignable_v<T&, const U&> is true,
is_constructible_v<T, optional<U>&> is false,
is_constructible_v<T, optional<U>&&> is false,
is_constructible_v<T, const optional<U>&> is false,
is_constructible_v<T, const optional<U>&&> is false,
is_convertible_v<optional<U>&, T> is false,
is_convertible_v<optional<U>&&, T> is false,
is_convertible_v<const optional<U>&, T> is false,
is_convertible_v<const optional<U>&&, T> is false,
is_assignable_v<T&, optional<U>&> is false,
is_assignable_v<T&, optional<U>&&> is false,
is_assignable_v<T&, const optional<U>&> is false, and
is_assignable_v<T&, const optional<U>&&> is
false.