I thought I understood ranges until I actually started trying to use them. Now I'm having difficulties with the new range-based containers. So I've got two issues right now, grokking ranges and understanding the container interfaces.

Given an SList, I want to do the following:

foreach(obj; list)
{
   if(obj.pleaseKillMe)
      somehow_remove_the_object_from_the_list();
}

Part of my problem is I'm not entirely clear what's going on with the foreach. I know it's iterating a range, but is it the SList itself being iterated, or is it a range returned by SList.opSlice? I assume the latter, which at one point led me to try this (thinking of Java's iterator.remove()):

auto r = list[];
foreach(obj; r)
{
   if(obj.pleaseKillMe)
      r.popFront();
}

Which, of course, didn't work. I see that popFront doesn't actually 'pop' anything off of, or out of, the range as it would in a traditional stack or a queue. The foreach doc says about range.popFront:

move the left edge of the range right one

Meaning, it's more like a next() than the pop() I'm familiar with (recalibrating all those years of C and Java terminology is not easy). And even if it did, changes to the range do not propagate to the underlying container. I understand that, at least (now).

So apparently I want something like the list.stableRemove*() variants, which the docs say remove an item from a container without invalidating any ranges currently iterating the container. Great! Only, there's no variant that accepts a single item. SList has removeFront and removeAny, and ranges can be removed via linearRemove. I can insert individual items fine. But how do I remove them?

Hello Mike,

> I want to do the following:
> foreach(obj; list)
> {
> if(obj.pleaseKillMe)
> somehow_remove_the_object_from_the_list();
> }

That isn't legal for normal arrays or AAs. IIRC the docs even say that you can't change what a foreach is iterating over during the foreach. I think you will have to convert to a manual for loop to make it work. That said, I've not worked with range at all.

-- 
... <IXOYE><

On Tue, 29 Jun 2010 07:16:13 +0200, BCS <none@anon.com> wrote:

> Hello Mike,
>
>> I want to do the following:
>> foreach(obj; list)
>> {
>> if(obj.pleaseKillMe)
>> somehow_remove_the_object_from_the_list();
>> }
>
> That isn't legal for normal arrays or AAs. IIRC the docs even say that you can't change what a foreach is iterating over during the foreach. I think you will have to convert to a manual for loop to make it work. That said, I've not worked with range at all.
>

Perhaps keep the foreach and make a list of to be deleted objects and then delete them after the foreach.

On Mon, 28 Jun 2010 23:01:42 -0400, Mike Parker <aldacron@gmail.com> wrote:

> I thought I understood ranges until I actually started trying to use them. Now I'm having difficulties with the new range-based containers. So I've got two issues right now, grokking ranges and understanding the container interfaces.
>
> Given an SList, I want to do the following:
>
> foreach(obj; list)
> {
>     if(obj.pleaseKillMe)
>        somehow_remove_the_object_from_the_list();
> }
>
> Part of my problem is I'm not entirely clear what's going on with the foreach. I know it's iterating a range, but is it the SList itself being iterated, or is it a range returned by SList.opSlice? I assume the latter, which at one point led me to try this (thinking of Java's iterator.remove()):
>
> auto r = list[];
> foreach(obj; r)
> {
>     if(obj.pleaseKillMe)
>        r.popFront();
> }
>
> Which, of course, didn't work. I see that popFront doesn't actually 'pop' anything off of, or out of, the range as it would in a traditional stack or a queue. The foreach doc says about range.popFront:
>
> move the left edge of the range right one
>
> Meaning, it's more like a next() than the pop() I'm familiar with (recalibrating all those years of C and Java terminology is not easy). And even if it did, changes to the range do not propagate to the underlying container. I understand that, at least (now).
>
> So apparently I want something like the list.stableRemove*() variants, which the docs say remove an item from a container without invalidating any ranges currently iterating the container. Great! Only, there's no variant that accepts a single item. SList has removeFront and removeAny, and ranges can be removed via linearRemove. I can insert individual items fine. But how do I remove them?

linearRemove is it for SList.  Sucks, but that's what's available, until Andrei can figure out a better way to remove a range.

With a singly linked list, you can't remove the front of a range, because you have to alter the element *before* the front element.  What SList needs is a function to allow removing all but the *first* element in the range.  Something like removeTail.  I think it would be an SList-specific function, not much use outside there.

Anything you use will have to avoid foreach, removing elements from anything while using foreach on that thing is not a good idea (unless the foreach is doing it for you, see below).  You have to manually handle the ranges.

You may want to give dcollections a try.  They support purging (the operation you are trying to write) natively with foreach via opApply.  The linked list is dual-linked, so there are no issues with removing arbitrary elements (removal of a single element is an O(1) operation):

LinkList!T list;

...

foreach(ref doPurge, obj; &list.purge)
{
   doPurge = obj.pleaseKillMe;
}

http://www.dsource.org/projects/dcollections

Please note, the online docs are D1 only, the D2 docs are included in the distribution, but aren't as pretty.

-Steve