Sylvain Pion <[EMAIL PROTECTED]> writes: > Dave, Jeremy, and Thomas, > > I have a suggestion for another "orthogonal" feature of iterators, which > is available for plain pointers : NULL. > More precisely, the fact that the default initialized iterator is a unique > (singular) value which you can reliably test equality with. > > It is very useful to have this capability : in the CGAL library, we store > the nodes of a graph in containers. Graphs are a bunch of nodes storing > pointers/iterators to each other. Having a value like NULL is very useful > there, because the alternative is either to allocate a specific object whose > iterator you use for this purpose (but it requires access to the associated > container to test with, which is painful), or storing a bool, which is a waste > of memory. > > I don't know if these issues arise in the BGL as well. > > I think this feature doesn't make sense for all iterators, especially for Input > and Output iterators. However, for iterators connected with containers, they > are usually trivial to provide because the iterator usually stores a pointer, > which can then be default initialized to NULL. > > In the case of CGAL, it would simply allow us to re-use the standard containers > for storing our graphs, while right now we re-implement containers...
What, specifically, would allow you to re-use the standard containers? I'm looking for a statement along the lines of, "if ... then we could re-use the standard containers". I'm guessing "..." is something like, "if default-constructed standard container iterators were non-singular and guaranteed to be unequal to any iterator obtained by other means". > > Another feature (less important but connected to the previous one) that > pointers have and iterators don't : automatic conversion to bool. > > What do you think ? It sounds like a useful concept, if I've understood you correctly. At the same time, I doubt it belongs in our proposal: we don't say anything about containers (except vector<bool>, and then only in the rationale). You should write a proposal for extension and submit it to the commitee if you care about this. It should be easy, compared to the iterator adaptors/categories proposal. -- Dave Abrahams Boost Consulting www.boost-consulting.com _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
