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

let var go letvargo at gmail.com
Fri Jun 10 12:30:34 CDT 2016

I respect that anti-goal, but I think being over-rigid about limiting
developers' choice of expression is also an anti-goal.

To me, it is like guard statements vs. if-let statements. Some people find
one to be more clear than the other. Often times the best choice depends on
the context. Sometimes a guard statement can be re-written as an if-let
statement in a way that makes the code more clear, and vice versa. And
different people will inevitably have different personal preferences -
their own "style", if you will - and will favor one over the other. But it
would be a mistake to force everyone into one box in order to prevent the
fracturing of the Swift community into "dialects."

But most importantly (and this is really the kicker for me) there are times
when the "where" syntax provides the maximum amount of clarity in the
context of my code, and I don't want to lose that expressive power.

On Fri, Jun 10, 2016 at 10:17 AM Xiaodi Wu <xiaodi.wu at gmail.com> wrote:

> 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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