Steven Schveighoffer wrote:
"Andrei Alexandrescu" wrote
Bill Baxter wrote:
On Mon, Jan 19, 2009 at 9:16 AM, Andrei Alexandrescu
<[email protected]> wrote:
Unless it's a class you mean?
Yah, ranges are meant to have value semantics. If you have a class
container
exposing ranges, define the range separately from the container itself:
MyIterable collection;
foreach (element; collection.all) {}
foreach (element; collection.all) {}
Add .opRange so that's not necessary? Or allow opApply to return a
range?
Otherwise it looks like a step backwards.
Why is it a step backwards? A given container may define a number of
ranges. Arrays are deceivingly simple because they have one obvious way of
iteration, but even for them you'd have to write:
int[] a;
foreach (element; a.retro) { ... }
I have to side with the others on this. foreach(element; collection) is so
damned intuitive ("for each element in a collection"), it should at least
try to call a default range function first, before trying to use collection
as a range. I'm for having opRange, and ditching opApply. I don't really
see the need for opApply (and I used a lot of forwarding opApply calls in
dcollections, so I'll probably have to rewrite that now!). You could also
write cool things like (for instance in a string-indexed collection):
foreach(element; collection["a".."m"])
instead of
foreach(element; collection["a".."m"].all)
Ok, I understand.
While we're on the subject of ditching, can we get rid of foreach_reverse?
How hard is it for a range to just have a reverse property:
foreach(element; myrange.reverse)
Which simply reverses the order of traversal? That also would moot the
toe/last/tail/etc. debate ;)
I wish that debate went away. But eliminating toe and retreat would
require requiring .reverse as a primitive for *all* ranges, which is
wasteful and repetitive. Instead, a better design is to have ranges
(those that can) offer toe and retreat primitives such that a generic
function retro offers backward iteration for any range. In addition,
certain algorithms (such as the one that reverses a range in place) need
to manipulate the same range from two ends. Implementing them using
.reverse and a second range would be more difficult.
Andrei
