[swift-evolution] repeat loop enhancement
Tyler Cloutier
cloutiertyler at aol.com
Wed Dec 9 15:46:58 CST 2015
Even better (shorter)
loop {
// code
}
loop for x in 0..<5 {
// code
}
loop for var i = 0 while someCondition(i) {
// code
}
loop for var i = 0 {
// code
} while someCondition(i) // The i variable would likely have to be considered in scope in the while expression
loop 5 {
// code
}
loop for var i = 0 while i < 5 {
// code
} always i += 1
> On Dec 9, 2015, at 1:29 PM, Tyler Cloutier via swift-evolution <swift-evolution at swift.org> wrote:
>
> Sorry, something is up with my email address.
>
>
> Oooh and one more, the Infinite Loop:
>
> repeat {
>
> }
>
>
>> On Dec 9, 2015, at 12:58 PM, Tyler Cloutier via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>
>> I’m still of the belief that all types of loops could be condensed down to a single type of loop, the repeat-for loop
>>
>> Consider:
>>
>>
>> The for-in loop:
>>
>> repeat for x in 0..<5 {
>> // code
>> }
>>
>> The C style for loop and the while loop:
>>
>> repeat for var i = 0 while someCondition(i) {
>> // code
>> }
>>
>>
>> The repeat while:
>>
>> repeat for var i = 0 {
>> // code
>> } while someConditionEvaluatedAfterFirstLoop() // The i variable would likely have to be considered in scope in the while expression
>>
>>
>> The currently discussed repeat loop
>>
>> repeat 5 {
>> // code
>> }
>>
>> All follow a very basic pattern: The repeat keyword followed by a for declaration of loop scoped variables, then either a condition in the case of while or an iterator in the case of for-in. Optionally the language could include an “always” keyword that would specify a set of statements that were guaranteed to execute after each run of the loop. For example:
>>
>> repeat for var i = 0 while i < 5 {
>>
>> } always i += 1
>>
>> If this were the case then all current loop constructs and their features could be subsumed by a single type of loop (including the to-be-removed C style for). This does have the problem of increasing the length of some current loop constructs though, specifically for-in.
>>
>> Tyler
>>
>>
>>
>>
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>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
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>>> On Dec 8, 2015, at 10:05 PM, André Videla via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>
>>> How about having a default implementation in the standard library for it?
>>> We avoid syntactic sugar and we allow for this very simple yet useful expression.
>>> And we’ve seen solutions in this thread using autoclosurses and extensions
>>>
>>> 5.times {
>>> …
>>> }
>>>
>>> or a function
>>>
>>> repeat(4) {
>>> …
>>> }
>>>
>>> all sound good to me.
>>>
>>> - André
>>>
>>>
>>>
>>>
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>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
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>>>> On 09 Dec 2015, at 06:58, Chris Lattner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>
>>>> On Dec 8, 2015, at 4:43 PM, Daniel Steinberg via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> For me this comes up when teaching children or new programmers. (Perhaps not a valid use case)
>>>>
>>>> This is a very valid use case.
>>>>
>>>> FWIW, “repeat N {}” was originally designed and scoped into the Swift 2 implementation of the feature, but was cut due to schedule limitations. There is precedent for this sort of feature in many teaching oriented languages (e.g. Logo).
>>>>
>>>> I’d say that the pro’s and con’s of this are:
>>>>
>>>> + Makes a simple case very simple, particularly important in teaching.
>>>> + Even if you aren’t familiar with it, you can tell at first glance what the behavior is.
>>>> - It is “just syntactic sugar”, which makes the language more complex.
>>>> - It is a very narrow feature that is useful in few practical situations.
>>>>
>>>> -Chris
>>>>
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>
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