On Jun 29, 2008, at 5:03 AM, Ion Gaztañaga wrote:
Gordon Woodhull wrote:
Hello, I am hoping to contribute an extension for intrusive to handle fusion containers, so that an intrusive hook can be an element in a fusion container and a fusion container can be an item in an intrusive container.
I have no idea about fusion, but you propose adding fusion_container_from_element to Intrusive, right? Correct me if I'm wrong, but I understand from the code that you first obtain the an iterator to an ElementKey (a type) of the map and then obtain a pointer to member to that element type inside the fusion container. Then you use offset_from_pointer_to_member function of Intrusive to obtain a pointer to the map.
Yes - that's what this code almost implements, except that the class template for which I'm able to get pointer-to-member is buried as private members a couple of layers deep, so it doesn't quite work.
I was thinking if offset_from_pointer_to_member could be pushed to somewhere more Boost libraries can use (to boost/detail perhaps?) and avoid having fusion<->intrusive dependencies. Then we can add fusion_container_from_element to Fusion.
That makes lots of sense to me - there are a few other uses for parent_from_member and container_from_member that definitely "ignore" C ++'s nice abstraction facilities but are nonetheless useful. "Overloading fields" with get/set methods on the parent class with zero overhead, for example. Black arts that can be made safe with some metaprogramming. (Doesn't necessarily make them always a good idea.) I'll just keep an image of changed/added files from intrusive, fusion, and detail in sandbox/metagraph since this is for that. And I'll post again when there's something for people to look at. Cheers, Gordon