[swift-evolution] repeat loop enhancement

[Liam Butler-Lawrence]

+1 for repeat X { } (as a keyword/statement, not a function).

It's definitely syntax sugar, but I agree it would give beginners an easy "in" to for loops. It would also make some of the code we write a bit smaller and more readable, which is always a good thing. I haven't seen any serious detriments put forward either.

Liam

Sent from my iPhone

> On Dec 9, 2015, at 8:30 AM, Daniel Steinberg via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Thanks Kenny
> 
> It’s so difficult for us to remember when these constructs weren’t familiar to us - to remember how much complexity there is in this code:
> 
>> 
>> for x in 1...5 {
>>    … some code…
>> }
> 
> for x in 1…5 - what does 1 … 5 mean? What does it mean for x to be in 1 … 5? Now you tell me x isn’t in 1 … 5 and I can replace x with _  what does it mean for _ to be in 1 … 5 and why do I need _ at all? _ isn’t in the loop either. What’s a loop?
> 
> That’s not to say I haven’t taught this - I’m saying it’s a lot harder for someone new to programming to grasp than many people think. 
> 
> I understand that it’s not a goal of the language to introduce syntax we only use in passing until they are ready to understand the for syntax so I won’t continue to argue the point. I was just voicing my support for the proposal and adding a use case where it might apply.
> 
> Best,
> 
> Daniel
> 
>> 
>> 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
>> 
>> -Kenny
>> 
>> 
>> 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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>>> swift-evolution at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> 
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