Linked list as a bidirectional range? I have some questions...

[Gary Willoughby via Digitalmars-d-learn]

On Monday, 11 August 2014 at 18:20:51 UTC, H. S. Teoh via 
Digitalmars-d-learn wrote:
> If you make your linked list container the same thing as a
> range over it, then iterating over the range will empty the 
> container as
> well, which generally isn't what you want.

Yes but only if it's been implemented purely as an input range. I 
was wondering if it was implemented as a forward range. Forward 
ranges allow iteration without destroying the contents. I was 
wondering how the 'save' method of the forward range could be 
implemented with a linked list. If my understanding is correct 
this method yields a copy to iterate over and discard.

> It's much better to separate the container itself from ranges 
> over the
> container. This then allows you to have separate container 
> methods that
> return ranges of different types.

That does answer it partially. This abstraction could return 
ranges over the nodes or items. but ultimately these have to 
expose the underlying data or provide a copy. (i.e. the 'save' 
method of forward ranges.)

Also iterating in reverse (which should be possible with a doubly 
linked list) such ranges will have to be bidirectional ranges.

These questions are all kind of inter-linked. I want to iterate 
forward and back through the list and if possible provide a nice 
public interface. It doesn't seem right to expose the nodes as 
that smells of a leaking abstraction. Hiding the nodes make it 
harder to iterate without a nice interface i.e. bidirectional 
range.

Ranges are nice but the (forward range's) 'save' method needs 
careful consideration. opApply is nice but i can't see a way to 
overload it for reverse iteration.