[swift-evolution] [Pitch] Retiring `where` from for-in loops

[Charlie Monroe]

> Moreover, I find it far cleaner to use the where clause that having to remember than I have to use the lazy accessor to avoid a performance hit.

See the benchmarks me and Erica have posted here a few days back - even with the lazy accessor, if you decided to use filter(_:), you lost 10+% of performance. Correct way to do this without `where` and without performance penalization is to use guard within the for-in loop.

> 
>> Le 13 juin 2016 à 06:39, Charlie Monroe via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>> 
>>> And to follow-up to myself once again, I went to my "Cool 3rd Party Swift Repos" folder and did the same search. Among the 15 repos in that folder, a joint search returned about 650 hits on for-in (again with some false positives) and not a single for-in-while use.
>>> 
>>> -- E
>> 
>> Not to undermine this fact, but I believe the fact that `where` can be used in a for loop is not widely known. I didn't know about it until about a month ago (haven't really read much docs, but most people don't either).
>> 
>> But after I found out about it, I started using it and it IMHO improved readability of my code. Not by much, but it's the little things that make you smile, right?
>> 
>> Many people here argument that `where` is a Swift speciality and needs to be learned by the developer - the alternative is to teach the person what's the proper alternative - that using .filter can have performance impact and that the *correct* way is to use guard within the for loop. And that's IMHO much worse than teaching a person about using `where` within a for loop.
>> 
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