On 12/3/17 12:42 AM, Johan Engelen wrote:
On Friday, 1 December 2017 at 18:33:09 UTC, Ali Çehreli wrote:
On 12/01/2017 07:21 AM, Steven Schveighoffer wrote:
> On 12/1/17 4:29 AM, Johan Engelen wrote:
>> (Also, I would expect "popFront" to return the element
popped, but it
>> doesn't, OK...
>
> pop removes the front element, but if getting the front
element is
> expensive (say if it's a map with a complex lambda function),
you don't
> want to execute that just so you can return it to someone who
doesn't
> care. This is why front and popFront are separate.
Yet, we're told that compilers are pretty good at eliminating that
unused copy especially for function templates where all code is visible.
I assume that Steven means "copying the front element" when he wrote
"getting the front element"?
No I mean generating the front element. For example:
auto m = [1, 2, 3].map!(a => reallyExpensiveFunction(a));
Each time you call front, it's going to be really expensive. If you
aren't going to use it, then generating it is wasted cycles.
(BTW, I said "pop" when I meant "popFront", sorry for *that* confusion too!)
There is no need for a copy, because the
element will be removed from the range, so we can move (whose cost only
depends on the size of the element, internal pointers being disallowed
by the language).
Yeah, this wasn't my concern, sorry for being ambiguous.
-Steve
