Class value_category_receiver

test/exec/asio/test_completion_token.cpp:699–747

  }

  struct value_category_receiver
  {
    using receiver_concept = receiver_tag;

    void set_value(std::mutex&&) && noexcept
    {
      CHECK(kind_ == kind::none);
      kind_ = kind::rvalue;
    }

    void set_value(std::mutex&) && noexcept
    {
      CHECK(kind_ == kind::none);
      kind_ = kind::mutable_lvalue;
    }

    void set_value(std::mutex const &) && noexcept
    {
      CHECK(kind_ == kind::none);
      kind_ = kind::const_lvalue;
    }

    void set_error(std::exception_ptr) && noexcept
    {
      CHECK(kind_ == kind::none);
      kind_ = kind::error;
    }

    void set_stopped() && noexcept
    {
      CHECK(kind_ == kind::none);
      kind_ = kind::stopped;
    }
    enum class kind
    {
      none,
      rvalue,
      mutable_lvalue,
      const_lvalue,
      error,
      stopped
    };

    constexpr explicit value_category_receiver(kind& k) noexcept
      : kind_(k)
    {}
   private:
    kind& kind_;
  };

  TEST_CASE("When the operation declares separate rvalue and lvalue completion signatures they are "
            "appropriately passed through",