popFrontExactly?

[Dmitry Olshansky]

11/23/2012 9:19 AM, Jonathan M Davis пишет:
> On Friday, November 23, 2012 03:55:21 Kapps wrote:
>> Is it really that big an issue to have a few more methods than
>> standard ranges would need? Before it certainly would be annoying
>> to have to check if the range supported it, use that, and if not
>> fake it, but now we have UFCS. It would be simple to have a basic
>> fallback implementation of methods such as popFrontExactly, then
>> simply use range.popFrontExactly to get the more performant one
>> if the range supports it, and if not get the fallback.
>>
>> It would have to be clear in the documentation that these are
>> optional methods however, and are recommended only if performance
>> is required (and if the range supports it in a way that isn't
>> simply an alternate implementation of the fallback).
>
> You misunderstood. popFrontExactly/popFrontNExactly wouldn't be on any ranges
> any more than popFrontN or drop are on any ranges. They're free functions in
> std.range which either slice a range or call its popFront in a loop (depending
> on the type of range) in order to pop the appropriate number of elements off,
> and popFrontNExactly would be the same.
>
> It may very well be that we should add popFrontNExactly in order to get that
> extra efficiency gain over popFrontN in the cases where you know that the range
> contains at least the number of elements being popped.

This gets interesting - how did you know it? The number of elements to 
pop I mean. I'd say the cases where hasLength is true and there is no 
slicing is quite rare. It'd be interesting to know what are these cases 
that it this set of helpers tries to speed up. I mean a list of:
-algorithms where popFrontN is used
-ranges that allow hasLength but not slicing and work with the said 
algorithm

And I agree with Jonathan that adding a bunch of helpers should be 
justified. Any helper function like say 'enforce' has utility only as 
long as simplifies a usage of a _frequent_ enough pattern.

If it simplifies/speed up certain algorithms there is no guilt in just 
using them internally.

-- 
Dmitry Olshansky