On Fri, 2008-04-11 at 09:40 -0400, Frank Mori Hess wrote:
On Thursday 10 April 2008 19:13 pm, Daniel Frey wrote:
I like that you call _internal_accept_owner on T* directly, still I think that I template class for tagging has some advantages. See the attached code I played with. In it, A has the role of the tag class. As the code shows, it is possible to have multiple classes like these, you just need some manual forwarding in the more complicated cases.
I don't understand what the benefit will be when applied to shared_ptr_observer? All I get from the example is that if you have a class X derived from A<T>, you can tell whether X and T are the same type or not. Manual forwarding works just as well without a template parameter. Maybe if you explained (as if writing user documentation for the feature) what the template argument of shared_ptr_observer is supposed to be set to, and what effect it would have? The behavior associated with a non-template shared_ptr_observer tag can be spelled out in 1 or 2 sentences.
I enhanced the example and added some comments. The reason for having a template tag class is that you can fix otherwise problematic cases when multiple tags are present. I don't think we can do the redirection automatically (except when someone adds compile-time reflection that allows us to iterator over the base classes), but at least there is a way to support this use case by a little bit of extra work. Regards, Daniel