Function make_optional

src/butil/containers/optional.h:413–415

// Creates a non-empty 'optional<T>`.
template <typename T>
optional<typename std::decay<T>::type> make_optional(T&& v) {
    return optional<typename std::decay<T>::type>(std::forward<T>(v));
}

template <typename T, typename... Args>
optional<T> make_optional(Args&&... args) {