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

[Xiaodi Wu]

I think this idea--if you don't like it, then you don't have to use it--is
indicative of a key worry here: it's inessential to the language and
promotes dialects wherein certain people use it and others wherein they
don't. This is an anti-goal.

On Fri, Jun 10, 2016 at 12:10 let var go <letvargo at gmail.com> wrote:

> Leave it in!
>
> It's a great little tool. I don't use it very often, but when I do it is
> because I've decided that in the context of that piece of code it does
> exactly what I want it to do with the maximum amount of clarity.
>
> If you don't like it, then don't use it, but I can't see how it detracts
> from the language at all.
>
> The *only* argument that I have heard for removing it is that some people
> don't immediately intuit how to use it. I didn't have any trouble with it
> at all. It follows one of the most basic programming patterns ever: "For
> all x in X, if predicate P is true, do something." The use of the keyword
> "where" makes perfect sense in that context, and when I read it out loud,
> it sounds natural: "For all x in X where P, do something." That is an
> elegant, succinct, and clear way of stating exactly what I want my program
> to do.
>
> I don't doubt that it has caused some confusion for some people, but I'm
> not sold that that is a good enough reason to get rid of it. It seems
> strange to get rid of a tool because not everyone understands how to use it
> immediately, without ever having to ask a single question. As long as its
> not a dangerous tool (and it isn't), then keep it in the workshop for those
> times when it comes in handy. And even if there is some initial confusion,
> it doesn't sound like it lasted that long. It's more like, "Does this work
> like X, or does this work like Y? Let's see...oh, it works like X. Ok."
> That's the entire learning curve...about 5 seconds of curiosity followed by
> the blissful feeling of resolution.
>
> On Fri, Jun 10, 2016 at 9:32 AM Xiaodi Wu via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> On Fri, Jun 10, 2016 at 11:23 AM, Sean Heber via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>
>>> > 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.
>>>
>>> Weird. My own Swift projects (not on Github :P) use “where” all the time
>>> with for loops. I really like it and think it reads *and* writes far better
>>> as well as makes for nicer one-liners. In one project, by rough count, I
>>> have about 20 that use “where” vs. 40 in that same project not using
>>> “where”.
>>>
>>> In another smaller test project, there are only 10 for loops, but even
>>> so one still managed to use where.
>>>
>>> Not a lot of data without looking at even more projects, I admit, but
>>> this seems to suggest that the usage of “where” is going to be very
>>> developer-dependent. Perhaps there’s some factor of prior background at
>>> work here? (I’ve done a lot of SQL in another life, for example.)
>>>
>>
>> That is worrying if true, because it suggests that it's enabling
>> 'dialects' of Swift, an explicit anti-goal of the language.
>>
>>
>>>
>>> I feel like “where” is a more declarative construct and that we should
>>> be encouraging that way of thinking in general. When using it, it feels
>>> like “magic” for some reason - even though there’s nothing special about
>>> it. It feels like I’ve made the language work *for me* a little bit rather
>>> than me having to contort my solution to the will of the language. This may
>>> be highly subjective.
>>>
>>> l8r
>>> Sean
>>>
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