[swift-evolution] SE-0045 status?

[Erica Sadun]

> On Jun 8, 2016, at 12:05 AM, Chris Lattner <clattner at apple.com> wrote:
> 
>> 
>> On Jun 7, 2016, at 9:54 PM, Erica Sadun <erica at ericasadun.com> wrote:
>> 
>> 
>>> On Jun 7, 2016, at 9:37 PM, Chris Lattner <clattner at apple.com> wrote:
>>> 
>>> 
>>>> On Jun 6, 2016, at 8:35 AM, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> Did we ever get to a stopping point on SE-0045, with the take while / drop while methods? I remember we were discussing using prefix / suffix and a bunch of other names, but was the consensus ever fully settled? I'm going back through the gmane archive, the SE repo, and the 5-31 dev build and can't seem to find anything on either one. I'm hoping I'm just missing something but fearing it never got settled. If not, I'd be happy to jump in and do the paperwork, but I'd really prefer if the two methods were there and I was just somehow overlooking them.
>>> 
>>> My understanding is that prefix(while:) and drop(while:) were accepted, per the rationale:
>>> http://thread.gmane.org/gmane.comp.lang.swift.evolution/16119
>>> 
>>> -Chris
>> 
>> After that was a lively discussion about rationalizing first/last/prefix/suffix/drop/take/etc. methods was there not?
> 
> Hah, entirely possible, who can say?  So much email! :-) :-)
> 
> -Chris

Here's where things seem to have ended up (thank you Guillaume!)

http://article.gmane.org/gmane.comp.lang.swift.evolution/16334/ <http://article.gmane.org/gmane.comp.lang.swift.evolution/16334/>

-- E

On Fri, May 6, 2016, at 06:05 PM, Dave Abrahams via swift-evolution wrote:
> 
> on Fri May 06 2016, Kevin Ballard <swift-evolution <at> swift.org> wrote:
> 
> > On Fri, May 6, 2016, at 05:31 PM, Kevin Ballard wrote:
> >> On Fri, May 6, 2016, at 05:19 PM, Dave Abrahams via swift-evolution wrote:
> >> > 
> >> > on Wed May 04 2016, Chris Lattner <swift-evolution <at> swift.org> wrote:
> >> > 
> >> > > Proposal link: https://github.com/apple/swift-evolution/blob/master/proposals/0045-scan-takewhile-dropwhile.md
> >
> >> > >
> >> > > Hello Swift Community,
> >> > >
> >> > > The review of SE-0045: "Add scan, prefix(while:), drop(while:), and
> >> > > unfold to the stdlib" ran from April 28...May 3, 2016. A subset of the
> >> > > proposal is *accepted, with modifications* for Swift 3.  This proposal
> >> > > included four new additions to the standard library:
> >> > >
> >> > > Sequence.prefix(while:) & Sequence.drop(while:) - These are *accepted* as specified in revision
3 of the proposal.
> >> > 
> >> > I know the review is over and all, but…
> >> > 
> >> > Chris brought to my attention an idea that I liked, and asked me to post
> >> > here about it.  Specifically, the argument label “where:” would probably
> >> > be better than “while:”.  “While” makes it sound to me like it's going
> >> > to take a nullary predicate and be much more active.  But it's hard to
> >> > love
> >> > 
> >> >      s.drop(where: { $0 > 1 })
> >> >      s.drop { $0 > 1 }
> >> > 
> >> > because it makes it sound like a general filtering operation.
> >> > 
> >> > Therefore, I'd much rather see
> >> > 
> >> >        s.droppingPrefix(where: {$0 > 1})
> >> 
> >> Using "where:" has a very high potential for confusion, because
> >> "where" makes it sound like it runs the predicate against every
> >> single element, whereas "while" makes it clear that it stops
> >> evaluating elements once the predicate returns false. Or in other
> >> words, `drop(where: predicate)` looks like it should be equivalent
> >> to `filter({ !predicate($0) })`.
> >
> > Oops, I read your message too fast and missed the fact that you
> > changed the function name too in the very last line.
> 
> And made the exact point that you made :-)

Indeed. My apologies, I was trying to get through my email too fast and ended up skimming too much.

> > If we switched to `droppingPrefix(where:)` then we'd need to change `dropFirst(_:)` as well.
> 
> Yes, as I noted in my response to Erica, I would like to see some more design
> coherence in this whole area.  I think
> 
>           xs.dropFirst()  =>  xs.droppingFirst()
>           xs.dropFirst(3) => xs.droppingPrefix(ofMaxLength: 3)
> 
> I'm not wedded to “dropping,” especially because it has other
> connotations.  Dmitri, Max, and I kicked around a bunch of other
> possibilities, e.g.
> 
>           sansPrefix
>           withoutPrefix

If we do rename this, I'm partial to basing it off of the word "skip", e.g. skippingPrefix(), since that's
similar to "drop" but doesn't have the connotation of possibly mutating the receiver. That said, having a
first argument label "ofMaxLength:" seems overly verbose. Don't forget that not everybody has the
benefit of Xcode code completion when writing Swift code.

> Anyway, we can't do all of that by the seat of our pants.  I personally
> wouldn't want to go any further than s.dropPrefix(where: ...)  without a
> new proposal/review.

Agreed, anything beyond that needs a full review. So back to the suggestion at hand.

I wrote up a whole long explanation for why I still think "while" is the better choice, and then I thought
about how this impacts `prefix(...:)` instead of `drop(...:)`, and in this context "where:" makes more
sense. `prefix(while:)` turns "prefix" from a noun into a verb, and the verb meaning of "prefix" is not at
all what we're doing with this operation. But `prefix(where:)` is still a noun and makes sense. And of
course if we have `prefix(where:)` then it's a bit odd to have `drop(while:)`, so we'd have to go with
`drop(where:)` or `dropPrefix(where:)`. So I guess I've now convinced myself while writing this email
that "where:" is the right choice :D

That said, given that we already have `dropFirst(_:)`, maybe we should go with `dropFirst(where:)`
instead of `dropPrefix(where:)`? Otherwise it's a bit odd to have both "dropFirst" and "dropPrefix" as
names. Admittedly, this same argument applies to the existing `drop(while:)` name too, and I don't have a
great explanation for that beyond the fact that I had a vague idea that dropFirst(_:) might be renamed to
drop(first:), though that can't actually happen because having both dropFirst() and drop(first:) is
hugely confusing, and it doesn't make sense to rename dropFirst() to drop().
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160608/56edfc70/attachment.html>