> On May 6, 2016, at 12:35 AM, Dmitri Gribenko <[email protected]> wrote:
>
> On Thu, May 5, 2016 at 5:11 PM, Nate Cook <[email protected]
> <mailto:[email protected]>> wrote:
>> Thanks for the feedback, Dmitri &co, this all looks excellent! I'll work on
>> updating the proposal.
>>
>>> On May 5, 2016, at 6:13 PM, Dmitri Gribenko <[email protected]> wrote:
>>>
>>> On Tue, May 3, 2016 at 8:57 PM, Chris Lattner via swift-evolution
>>> <[email protected]> wrote:
>>>> Hello Swift community,
>>>>
>>>> The review of "SE-0078: Implement a rotate algorithm, equivalent to
>>>> std::rotate() in C++" begins now and runs through May 9.
>>>
>>> Hi,
>>>
>>> I'm posting this feedback on behalf of Dave Abrahams, Max Moiseev and
>>> myself. We met and discussed the proposal in great detail.
>>>
>>> First of all, we want to thank Nate and Sergey for proposing this API,
>>> which is an important and useful algorithm. We are generally in favor
>>> of the proposal, but we would like to request a few changes.
>>>
>>> Could you make 'func rotate' a requirement in the MutableCollection
>>> protocol? This allows selecting the best implementation for a given
>>> concrete type, even when calling from generic code.
>>>
>>> Could you explain why do we need a special implementation of
>>> 'reverse()' for RandomAccessCollection? We couldn't think of a
>>> performance reason for this.
>>
>> With a bidirectional collection, you have to compare the high and low index
>> at each iteration, stopping when low >= high (before indices were
>> Comparable, this required two equality comparisons per iteration). With a
>> random-access collection, you can optimize the loop to use a fixed number of
>> iterations, which should be more efficient.
>
> Good point! In that case, 'reverse()' should also be a protocol
> requirement, to allow dispatch to the most efficient version.
That brings up the question of which protocol to add the requirement to?
Without a MutableBidirectionalProtocol (which we don't want, right?), we'd need
to add it to MutableCollection. While a mutating reverse() is possible for a
forward collection, it has significant space complexity, since it works either
by creating an array of the indices or through recursion. We would also have
reverse() available on some collections that don't have reversed(). Does that
sound alright?
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <[email protected]
> <mailto:[email protected]>>*/
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
