--- On Fri, 5/6/11, Rene Rivera wrote:

On 5/6/2011 4:22 PM, Cromwell Enage wrote:

...

What are your thoughts on a generalized depth-first iterator that also indicates whether it's currently in pre-order traversal mode, post-order traversal mode, or neither?  I've found it useful for implementing scene graphs, for example.

The goal was to make it possible to have any kind of iteration.  The ones in the TR are the simple common ones.  So yes, other iterations would be good to add. I'm all for generalization.  Are you thinking of the static kind, as in traits, etc.?  Or are you thinking of something run-time?

I was originally thinking of run-time generalization, i.e. the depth-first iterator being a functional superset of pre-order, post-order, and in-order iteration.  But now that I look at the implementation, it might not necessarily be so.  For a simple illustration, consider this ASCII rendition of the following tree: ___B +--+--+ A_____C If this were stored in a sorted binary tree, one might expect binary_tree::iterator to output the elements in this order: A B C However, if we expect an unsorted nary_tree::iterator to behave the same way (in-order, in this case), then what is the correct output for the following tree? _________I +-----+--+--+-----+ A_____E_____O_____U My current depth-first iterator would output the following: I pre_order A pre_order A post_order E pre_order E post_order O pre_order O post_order U pre_order U post_order I post_order One could filter by pre_order or post_order to obtain the corresponding output, so in that respect my depth-first iterator would be a functional superset. However, it traverses every node exactly twice, and definitely not in the same way as a sorted binary_tree::iterator. Therefore, while I agree that my depth-first iterator could make a fine addition, it may not necessarily serve well as an nary_tree::iterator. Thoughts? Cromwell D. Enage