Filtering iterators

[akiross]

Deleting the pointed item invalidates the iterator. So does addition in certain cases.

My point is that the iterator/container/whatever can only work on const objects. And you can't modify those.

Modification doesn't regard only creation and deletion. There is also modification which doesn't invalidate iterators. Anyway, *this was not the point* and you went on another topic. The point was: if you use iterators for filtering, and data is highly mutable (NOT while iterating), then caching is useless and iterators are Ok to use.

Yeah, I call them generators If something generates something then it is a generator. If you want to iterate over a generator, that's fine but the iterator iterates, not generates, if you ask me. I know it's just a matter of taxonomy but still.

Probably you didn't read well what I wrote OR I expressed badly. I said:

I think that in case of "infinite iterators", for example when data is generated from external devices, network or pipelined algorithm, containers would be pointless.

I didn't say that iterators were used to generate data (and I thought that was obvious). A stream is not an iterator, but is an infinite source of data. I was talking about using iterators OVER an infinite collection of data, and as you say: "if you want to iterate over a generator, that's fine". And that was the point of my statement in first place.

If it has end() defined, then it is finite. Otherwise I hate to be in a skin of a person trying to process every element of such collection.

I don't agree. You're assuming that we are talking about STL-style iterators, which uses begin() and end(). Java-style iterators, for example, checks using "hasNext()" and not testing if they reached a defined end. That method could return true to give an infinite iterator.
In addition, I think that the semantic of the "end" method in STL iterators is NOT do define a length of a container, but to define a case in which has no longer sense to go on (which is very very different from saying that the iterator will find an end).
It's easy to build a circular list with >0 elements which will iterate forever, even if the end() is defined.
~Aki