[swift-evolution] repeat loop enhancement

[Daniel Steinberg]

For me this comes up when teaching children or new programmers. (Perhaps not a valid use case)

I'm not ready to introduce for but repetition is a useful notion. I used to add repeat() in an extension to Int

5.repeat{ ...}

Is easier to describe than 

for _ in 1...5 {...}

The _ and 1...5 are wonderful for us but often cause newbies to stumble

Now that repeat is a keyword I haven't come up with a good replacement yet

Daniel

> On Dec 8, 2015, at 6:21 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I've also thought of this idea before, but how often in code do you actually repeat something a given number of times? There are only a few use cases I can think of:
> 
> - retries before giving up on something
> - emitting padding when doing formatted output of some kind
> - reading formatted data when you have a given number of rows/records to read
> 
> If it's that rare, I'm not sure it's worth dedicating syntax to.
> Jordan
> 
>> On Dec 8, 2015, at 13:54, 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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> 
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