jat@xavax.com (John Tamplin) (05/06/90)
In article <763@orthogo.UUCP> basti@orthogo.UUCP (Sebastian Wangnick) writes: >>In article <1145@acf5.NYU.EDU> jjb3281@acf5.NYU.EDU (Thanbo) writes: >>>I would like to implement an iterator in C++ that would operate much >>>like a FOR loop: >>> >>>IntArray v; >>>v.for(int from_val, int to_val, int increment_amount, { C++ statement }); Why can't you do something like the following: { List list; ListIterator li; ListElem *le; for(li.first(list); le=li(); li.movenext()) { ... } } With each of my "abstract" classes like list, queue, stack, etc., I also build iterator classes for them. The only problem I have with this approach is that you have to do ugly casts to get the list elements to the proper type. Until parameterized classes comes along, I'm not sure that you can solve that anyway. What kind of iteration would you want to do that doesn't involve initialization, test, and increment steps? The proposed syntax above requires rather sticky syntactical notions of being able to pass an arbitrary chunk of code as an argument to a member function. The implementation should be easy, since the compiler could just make it a hidden function. But what do you do if you want to return a value? All this gets to really wanting to specify the function type, which you can do today in C++ if you write the function yourself. ie: v.iterate(int from_val, int to_val, int increment_amount, void (*func)()); In summary, I think the current language (although parameterized classes would certainly be nice) introduces only slight inconvenience in implementing iterators. -- John Tamplin Xavax jat@xavax.COM 2804 S Memorial Parkway ...!uunet!xavax!jat Huntsville, AL 35801