[swift-dev] C-style For Loops

[Dave Abrahams]

> On Dec 19, 2015, at 1:20 PM, Wallacy <wallacyf at gmail.com> wrote:
> 
> Curiously I was analyzing this part of the library a few minutes ago.
> It will probably be necessary to extend "Range":
> 
> extension Range where Element: Strideable {
>     func by(n: Element.Stride) -> StrideThrough<Element> {
>         return startIndex.stride(through: endIndex, by: n)
>     }
> }

Why?

> The first thing that came into my head was:
> 
> var rangeA = -150.0..<150 // HalfOpenInterval<Double>
> var rangeB = -150.0...150 // ClosedInterval<Double>
> var rangeC = -150..<150 // Range<Int>
> var rangeD = -150...150 // Range<Int>
> 
> For "Range" we need to use startIndex and endIndex respectively, and with HalfOpenInterval/ClosedInterval only start and end.
> 
> I do not know for you, but it seems inconsistent and redundant to me.

I don't understand most of what you're saying here, or why you're saying it.  The extensions as shown in Donnacha's post work for me.

> 
> Em sáb, 19 de dez de 2015 às 18:39, Dave Abrahams via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> escreveu:
>> On Dec 19, 2015, at 11:44 AM, Donnacha Oisín Kidney via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> 
>> You can define an extension on interval types:
>> 
>> extension HalfOpenInterval where Bound: Strideable {
>>   func by(n: Bound.Stride) -> StrideTo<Bound> {
>>     return start.stride(to: end, by: n)
>>   }
>> }
>> 
>> extension ClosedInterval where Bound: Strideable {
>>   func by(n: Bound.Stride) -> StrideThrough<Bound> {
>>     return start.stride(through: end, by: n)
>>   }
>> }
>> 
>> Which maybe gives you slightly more elegant usage:
>> 
>> for lat in (CGFloat(-60)...60).by(30) {
>>   print(lat)
>> }
>> 
>> for lat in (CGFloat(-60)..<60).by(30) {
>>   print(lat)
>> }
> 
> This is nice; why don't we put it in the standard library and get rid of the "stride" methods?
> 
>>> On 19 Dec 2015, at 18:59, Gavin Eadie via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>>> 
>>> With C-style for loops to be removed from the language to general acclaim (including mine), is the following the best way to perform the required looping:
>>> 
>>>     for lat in (CGFloat(-60.0)).stride(through: +60.0, by: 30.0) {
>>>         path.moveToPoint(CGPointMake(-180.0, lat))
>>>         path.lineToPoint(CGPointMake(+180.0, lat))
>>>     }
>>> 
>>>     for lon in (CGFloat(-150.0)).stride(through: +150.0, by: 30.0) {
>>>         path.moveToPoint(CGPointMake(lon, +90.0))
>>>         path.lineToPoint(CGPointMake(lon, -90.0))
>>>     }
>>> 
>>> That seems a slightly cumbersome usage.  Is there a better way to initialize the SequenceType I want to iterate over?
>>> 
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>> 
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> -Dave
> 
> 
> 
> 
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-Dave



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