> Le 23 mars 2016 à 21:59, William Dillon <[email protected]> a écrit :
>
>>
>> On Mar 23, 2016, at 6:46 PM, Dany St-Amant via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>>
>>> Le 22 mars 2016 à 21:19, William Dillon <[email protected]
>>> <mailto:[email protected]>> a écrit :
>>>
>>>>
>>>> These may be compact, but some programmer may fell that they are not in
>>>> control: do these "stdlib" seq(), c.filter() pre-calculate all the entries
>>>> (wasting precious cpu cycle if one break out early) or are each value
>>>> dynamically created? Having an explicit legacy loop format gives a feel of
>>>> control. So something like
>>>>
>>>> for i from 2 to 1_000_000 by 1 where i % 2 != 0 while foundCount < 5 {
>>>> print(i); foundCount +=1 }
>>>>
>>>> sounds less magical and seems easier to predict than
>>>>
>>>> for i in 2.stride(to:1_000_000, by:1).filter({ $0 % 2 != 0}).prefix(5) {
>>>> print(i) }
>>>>
>>>> and is still quite readable, even if it mixes for loop, while loop and
>>>> even simple condition.
>>>>
>>>
>>> I disagree. I think the first case is venturing dangerously close to the
>>> AppleScript “uncanny valley” of human language-like programming verbs where
>>> I never know the exact words and exact order for things. The second
>>> example is right out of any functional programming mold, and I fully
>>> understand what’s happening, and how to decompose the process to test
>>> assumptions. Also, I know how to implement the second case (more or less)
>>> from scratch, and that’s pretty huge for me.
>>>
>>
>> There have been multiple fights over too verbose versus too terse, and on
>> whether or not making it sound like English. I would agree a verbose syntax
>> for a mandatory statement is a pain, but the while and where above are
>> optional. And using them instead of relying on continue or break allow for
>> code intent to be bit clearer.
>>
>> Reusing my bad example, without the from/to/by:
>>
>> for i in 2.stride(to: 1_000_000, by: 1)
>> {
>> if i % 2 != 0 { continue }
>> print(i)
>> foundCount += 1
>> if foundCount >= 5 { break }
>> }
>>
>> // Where clause already work in current Swift
>> for i in 2.stride(to: 1_000_000, by: 1)
>> where i % 2 == 0
>> {
>> print(i)
>> foundCount += 1
>> if foundCount >= 5 { break }
>> }
>>
>> // While do not exist yet in this context
>> for i in 2.stride(to: 1_000_000, by: 1)
>> where i % 2 == 0
>> while foundCount < 5
>> {
>> print(i)
>> foundCount += 1
>> }
>>
>
> The ‘where’ I can tolerate because there are other examples of such a
> construct in other parts of the language. The while part is still
> problematic, because where have you declared it? Do you think declaring a
> variable for that somewhere outside the context of the loop is cleaner than
> leaving it entirely within that scope then doing a test and break?
Usually when a loop exit early with a break, which would make sense to use with
the while construct, such loop is followed by a if statement against that
condition, so it make perfect sense to declare it i the outer scope.
// While do not exist yet in this context
for i in 2.stride(to: 1_000_000, by: 1)
where i % 2 == 0
while foundCount < 5
{
print(i)
foundCount += 1
}
if foundCount != 5
{
print("Sorry not enough element for the quintuplet!.")
// return or throw... we don’t want to continue.
}
Anyway, you cannot declare the above foundCount inside the loop, as it would
get re-initialized on every iteration.
The for/in/while is not a replacement for some multiple variables loop:
for(x=0,y=1;…;…) but for some dual comparison loop (max and early exit):
for(…;i<max && !found;…)
Dany
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
