Proposal: takeFront and takeBack

[Roman D. Boiko]

On Tuesday, 3 July 2012 at 17:40:24 UTC, Jonathan M Davis wrote:
> On Tuesday, July 03, 2012 17:31:21 Christophe Travert wrote:
>> takeFront implementation is dangerous for ranges which 
>> invalidates their
>> front value when popFront is called, for instance, 
>> File.byLine. Thus
>> takeFront will have to be used with care: any range implement 
>> takeFront
>> (because of the template and USFC), but it may not be valid. 
>> That makes
>> the range interface more complicated: There is a takeFront 
>> property, but
>> you have to check it is safe to use... how do you check that 
>> by the way?
>
> Hmm. I hadn't thought of that. That could be a good reason not 
> to do this. I'm
> not quite sure how to get around that. Hmmm... It would 
> arguably be a bit
> ugly, but a range which couldn't safely be used with takeFront 
> could have an
> enum on it which indicated that, and takeFront would fail to 
> compile if used
> with such a range. Of course, that would mean that you'd have 
> to special case
> such ranges in any range-based function which used takeFront so 
> that there was
> a branch which didn't use takeFront for ranges which couldn't 
> use it.
>
> I don't know. It's certainly something to think about. We may 
> need a different
> solution.

An alternative is not to define a free function. So if 
consumeFront is defined, it may be used by the algorithm, 
otherwise simply call to front and popFront in the algorithm. If 
branching is necessary, then the is no value in a free function 
(it wouldn't optimize for speed any way).