Hi Joaquin, On Nov 27, 2008, at 9:34 AM, joaquin@tid.es wrote:
Gordon Woodhull escribió:
There is some scary code in parent_from_member but AFAIK it works everywhere.
Not everywhere, I'm afraid:
A-ha, I see. Bummer. I might have to debug it on a couple of platforms to use it for my purposes then. Metagraph can be thought of as a multicontainer extension to MultiIndex, or as a heterogeneous extension to Graph. I am using Fusion to compose objects out of their data and Intrusive hooks, so I need a fusion::container_from_element. I am trying to think whether I could adapt Fusion to use the very nice multi_index::detail::pod_value_holder approach, but I don't see it because Fusion uses containment (member variables) rather than inheritance for composition. I assume that's more efficient at compile time (?)
There are definitely some seriously non-standard tricks there that should IMHO discourage us from using parent_from_member unrestrictedly, useful as this utility may be.
I am not as scared by the tricks (they are nicely contained) as by the violation of abstraction. OTOH it's interesting to note that only the class or a friend can grant permission to do parent_from_member for a private member, because access is checked when the member address is taken. I believe iterator_to functionality does justify the danger of parent_from_member, when properly guarded. Thanks for the heads-up and the link, Gordon