Are iterators and ranges going to co-exist?

[Steven Schveighoffer]

On Sat, 24 Jul 2010 09:01:14 -0400, Jim Balter <Jim at balter.name> wrote:

>
> "Steven Schveighoffer" <schveiguy at yahoo.com> wrote in message  
> news:op.vf5kynqgeav7ka at localhost.localdomain...
>> On Tue, 20 Jul 2010 09:52:00 -0400, Andrei Alexandrescu  
>> <SeeWebsiteForEmail at erdani.org> wrote:
>>
>>> On 07/20/2010 03:01 AM, Peter Alexander wrote:
>>>> Some more arguments for iterators/cursors:
>>>>
>>>> 1. How would you implement Floyd's cycle finding algorithm using  
>>>> ranges?
>>>> (http://en.wikipedia.org/wiki/Cycle_detection#Tortoise_and_hare)
>>>> It uses two iterators over the same range. You would have to  
>>>> wastefully
>>>> use 2 ranges that have the same end coordinate.
>>>
>>> I think there's a confusion somewhere. You may want to check out the  
>>> SList definition in std.algorithm. A SList range is exactly one  
>>> pointer thick. With singly-linked lists it's the iterator approach  
>>> that is wasteful because it canonically transports a null pointer as  
>>> end().
>>
>> That is an example of a single exception to the rule :)  AFAIK, no  
>> other container types have ranges with no end pointer or length.
>
> zstrings, pipes, and various other streams.

Streams are in a completely different category.  They are not containers.

I personally feel that imposing the range/iterator/cursor idiom on top of  
a stream is a problematic model that's only done "because you can."  Kind  
of like the one-liner qsort in a functional language.

> Various calculated numeric series.

Those don't have ends afaik, and are read-only.  Take works perfectly fine  
in those cases where you need "n elements", in which case you have an end  
point ;)

> Ropes and other binary trees (threaded trees can be traversed with a  
> single pointer and no stack).

I'm not familiar with the internal structure of Ropes.

Look, technically, any node-based container can have a single-pointer  
range, but it leaves you with only one type of range -- one that goes to  
the end.  That doesn't sound very useful to me.

> Probably other classses of containers. And while SLists are "so (sic)  
> unique",

I meant 'so'

> very large amounts of very sophisticated code have been written using  
> just that "limited" datatype.

No, SList is brand new, not much code has been written with it ;)  You may  
object, but try using it and see how far it takes you.  SList is like a  
normal singly linked-list but with all the power removed for safety  
reasons.

-Steve