Method has_value

dlib/optional.h:624–624

        constexpr const T&& operator*() const&& noexcept { return std::move(this->val); }
        constexpr explicit  operator bool() const noexcept { return this->active; }
        constexpr bool      has_value()     const noexcept { return this->active; }

        constexpr T& value() & 
        {