Merge "FTL: Provide definition of BaseFuture where third template parameter is...

struct ValueTag {};

template <typename, typename T, template <typename> class>

class BaseFuture;

template <typename Self, typename T>

class BaseFuture<Self, T, std::future> {

  using Impl = std::future<T>;

template <typename Self, typename T, template <typename> class FutureImpl = std::future>

class BaseFuture {

 public:

  Future<T, std::shared_future> share() {

      return {ValueTag{}, std::move(*value)};

    }

    return std::get<Impl>(self()).share();

    return std::get<FutureImpl<T>>(self()).share();

  }

 protected:

      return std::move(*value);

    }

    return std::get<Impl>(self()).get();

    return std::get<FutureImpl<T>>(self()).get();

  }

  template <class Rep, class Period>

      return std::future_status::ready;

    }

    return std::get<Impl>(self()).wait_for(timeout_duration);

    return std::get<FutureImpl<T>>(self()).wait_for(timeout_duration);

  }

 private: