On Wednesday, 7 October 2015 at 17:13:45 UTC, Jonathan M Davis
wrote:
As I understand it, there are algorithms that inherently need 3
iterators to do whatever is they do, and the question of how to
deal with them has come up before in the newsgroup. I think
that it's pretty clear that such algorithms are relatively few
in number, but they do exist, and solving them with ranges does
get potentially awkward. Similarly, using iterators with
containers when you have to pass them to the container
generally works better than ranges do. We've had to add
overloads to the std.container types which take the results of
the various take functions in order to work around that
problem. So, there are clearly cases where ranges become
awkward and iterators aren't.
On the other hand, when dealing with algorithms, ranges tend to
be far cleaner - especially when you need to chain them. And
they tend to form a better basis of how to think about
algorithms (even when dealing with iterators, you pretty much
have to think in terms of ranges on some level at least). And
ranges handle laziness far better than iterators do. So, I'm
not the least bit convinced that iterators are a better way to
go (quite the opposite), and I'm not convinced that trying to
mix iterators and ranges is at all a good idea. But I do think
that it's clear that using only ranges is not without its
downsides, and since we're the first folks to seriously use
ranges heavily in a language or standard library, we're bound
to be making mistakes due to inexperience. At this point, I
would guess that trying to mix iterators and ranges is just
going to over-complicate things in an already over-complicated
language, but it may actually be a big win for the C++ folks.
We'll have to wait and see.
If we _were_ to look at doing something more than straight
ranges, we'd probably look more at something like Steven's
cursors than adding iterators, though I think that there's a
decent chance that that only really helps with containers (it's
been a while since I looked at what he did with cursors, and I
really don't remember the details), though for the most part, I
think that containers are the primary place where ranges tend
to get annoying. Algorithms where they're problematic do exist,
but they seem to be rare.
- Jonathan M Davis
Couldn't we define a TriRange or something for this?
