allocator template example in rclcpp

snippet.cpp

template<typename MessageT, template<typename> class Alloc = std::allocator>
class Publisher : public PublisherBase
{
  // ...
  Alloc<MessageT> message_allocator_;
  // Publisher doesn't have any STL structures, but suppose it did (or think about the case for services):
  std::vector<AnotherType, Alloc<AnotherType>> my_vector_;
  // ...
  void my_function() {
    // instead of MessageT * msg = new MessageT;
    MessageT * msg = std::allocator_traits<Alloc<MessageT>>::allocate(message_allocator_, 1);
  }
}