[swift-evolution] repeat loop enhancement

Kenny Leung kenny_leung at pobox.com
Tue Dec 8 23:10:02 CST 2015

Why don’t you just do

for x in 1...5 {
	… some code...

If you’re teaching to newcomers:

- there’s no need to explain that counting starts at 0 because it doesn’t
- if “x” is not used within the loop, then they will get a warning. That would be the perfect time to explain that they can just replace index with “_” when you don’t need to use the value within the loop.

BTW, I hate the “in x ..< count” syntax. If you mean count from 0 to 4, then just write 0…4


Excerpt From: Apple Inc. “The Swift Programming Language (Swift 2 Prerelease).” iBooks. 

> On Dec 8, 2015, at 1:54 PM, Jason Pollack via swift-evolution <swift-evolution at swift.org> wrote:
> I'd like to propose a small enhancement to the repeat loop.
> Currently if we want to perform 'count' iterations in a loop, we need to do something like:
> for _ in 0 ..< count {
>    //Do something here
> }
> It looks and feels a little awkward. We need to create an unnamed variable, and it's easy to forget (especially for language newcomers) that the loop starts with 0 and doesn't include count.
> We can also do:
> var i = 0
> repeat {
>     //Some code
>     i += 1
> } while i < 10
> This is worse, in that it introduces a variable in the outer scope, and puts the repeat count at the end. Plus, if the expression inside the repeat is complex, the value of i may never be incremented, or may be incremented more than once.
> I propose the following:
> repeat count {
>     //Do something here
> }
> It's cleaner, and IMO clearer what this code is intended to do.
> Naturally 'count' should be non-negative. A while clause is not needed, although I could imagine it being supplied, to create a construct such as:
> var ok = true
> repeat numberOfTimes {
>     //Do something, possibly set ok to false
> } while ok
> This would repeat the loop a maximum of  'numberOfTimes', but could be ended early if some signal 'ok' is set to false (or, of course, by a break statement).
> Thoughts?
> Thanks!
> -Jason-
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