[swift-evolution] [Review] SE-0078: Implement a rotate algorithm, equivalent to std::rotate() in C++

[Dmitri Gribenko]

On Thu, May 5, 2016 at 5:11 PM, Nate Cook <natecook at gmail.com> 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 <gribozavr at gmail.com> wrote:
>>
>> On Tue, May 3, 2016 at 8:57 PM, Chris Lattner via swift-evolution
>> <swift-evolution at swift.org> 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.

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 <gribozavr at gmail.com>*/