message: Make typed actor comparable to nullptr_t
diff: @@ -301,6 +301,30 @@ bool operator!=(const typed_actor<Xs...>& x,
  return !(x == y);
  }
  +/// @relates typed_actor
  +template <class... Xs, class... Ys>
  +bool operator==(const typed_actor<Xs...>& x, std::nullptr_t) noexcept {
  + return actor_addr::compare(actor_cast<actor_control_block*>(x), nullptr) == 0;
  +}
  +
  +/// @relates typed_actor
  +template <class... Xs, class... Ys>
  +bool operator==(std::nullptr_t, const typed_actor<Xs...>& x) noexcept {
  + return actor_addr::compare(actor_cast<actor_control_block*>(x), nullptr) == 0;
  +}
  +
  +/// @relates typed_actor
  +template <class... Xs, class... Ys>
  +bool operator!=(const typed_actor<Xs...>& x, std::nullptr_t) noexcept {
  + return !(x == nullptr);
  +}
  +
  +/// @relates typed_actor
  +template <class... Xs, class... Ys>
  +bool operator!=(std::nullptr_t, const typed_actor<Xs...>& x) noexcept {
  + return !(x == nullptr);
  +}
  +
  /// Returns a new actor that implements the composition `f.g(x) = f(g(x))`.
  /// @relates typed_actor
  template <class... Xs, class... Ys>
  