On Friday, 23 November 2012 at 15:48:04 UTC, Dmitry Olshansky
wrote:
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.
Usually, either by a previous iteration, or just because it is
statically know the range will have that many elements. Or that
it *should* have that many elements.
You could ask the question the other way around: Why would you
pop a certain amount of elements, if you don't even know your
range actually *holds* that many elements? Why do you even need
the safeguard in the first place?
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
What about the case of plain bidirectional ranges? That's the one
that's being sped up.
Still regardless of performance, the (my) motivating factor is
that when you use "drop", it pretty much silently fails if your
range doesn't have the amount of elements. IMO, in the long run,
this makes "drop" *un*-safe...
