[swift-evolution] [Proposal] Add keyword "by" as syntactic sugar to streamline For-In-loop

[Vladimir.S]

Right now it seems for me that for-in + "step" is the best solution that 
provides what we need with minimal changes :

for i in 0..<10 step 2 {
}

for i in 0..<10 step -2 {
}

for i in 0.1..<10.5 step 0.5 {
}

("step" is optional)

i.e. like current for-in loop, but with additional features.


On 14.04.2016 2:46, Ted F.A. van Gaalen wrote:
> Hi Vladimir,
>
> In the past weeks, I wrote extensively on swift-evolution
> about an alternative for the classical for-loop.
> So extensively that it irritated the ”Collectians”
> who (indirectly) classified me and some similar others
> as “Forloopians” and also “Traditionalists”…
> I consider this as a great honor. :o)
>
> Anyway, among other alternatives, I wrote this on April 5th.2016:
>
>> So, to me the best option is still to bring the for ;; back
>> or to make a new Swift equivalent for it as described here again.
>>
>> for d from 10.0 to 5.0 by -0.1 tolerance 0.01  //tolerance is optional
>> {
>>     print(d)
>> }
>
>
>      for v from v1 to v2 by vstep       // it can’t be any simpler than this.
>
> Of course, working with ALL existing numerical types, Int, Float, Double..
> ( Btw. me wishing: consolidate all floating point types into just one type,
> preferably Double!)
>
> Apart from the “tolerance”  option, which I intended for float boundaries
> in for-loops,
> this is not my really original idea, because the traditional for-loop exist
> more or less like this in most program languages for decades.
>
> What do you think about my suggested for-loop?
>
>
> I don’t like this variant at all:
>
>> for i in (1...10).striding(by: 3) {..}
>> for i in (1...10).striding(by: -3) {..}
>
> It is downright ugly, cumbersome to write,
> hard to read and also functionally very limited:     **
> - ranges like (10…-5)  are not allowed
> - ranges / for..in..  with other numerical types like Float and Double are
> not possible!
> - I am still doubtful about optimization:
>          the compiler always has to look what is behind the “in”
>
> Ergo: There is still no good alternative for the classical for ;;  that was
> in Swift.
>
> One has to use “while {...}” loops.
> which means specifying an iteration in 3 lines more and a bigger change
> for errors.
>
>
>> But.. compare how the next is more clear and nice looking, has less noise,
>> how faster this will be typed.. :
>>
>> for i in 1...10 by 3 {...}
>> for i in 1...10 by -3 {…}
>
> This looks better, indeed,
> but still has the same severe limitations **
>
>
>> My opinion: this .striding is about Range type. Range type is used in many
>> places, not just in for-in loop. It is important to have handy and clear
>> methods for Range. But. If we are talking about loop - why(why?) can't we
>> have such a great syntax for such a common loop task?
> That is my honest opinion too.
>
>  The only ambition of the for-loop I presented is for it
>  to be a convenience construct for the “while” loop
> which it has always been. it is actually the sole
> reason why it was invented in the first place.
>
> There is nothing to be ashamed of to bring back
> the for ;; . I am very serious here.
>
> It is (was) one of the most powerful control statements in Swift!
>
> IMHO it amazes me that people go through so much
> unnecessary effort in an attempt to replace / circumvent
> a nearly perfect iteration statement.
>
> But I wrote about all this already too many times.
>
> Please note that I do also see many good things and developments in Swift!
>
> met vriendelijke groeten
>
> TedvG
>
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