[swift-evolution] Reduce with inout

[Xiaodi Wu]

Yes, Matthew, I agree with you exactly on this. It's tricky. `copyOf` isn't
ideal at all, but `mutating` is potentially misleading. Ah the difficulties
of naming things.


On Tue, Jan 24, 2017 at 09:15 Matthew Johnson <matthew at anandabits.com>
wrote:

> On Jan 24, 2017, at 8:12 AM, Chris Eidhof <chris at eidhof.nl> wrote:
>
> But if we want to add "copyOf" we should do that to every method that
> takes a struct? Also, what if you pass in an object?
>
> I see the concern, but I don't think adding `copyOf` will increase
> clarity. That said, I'm open to suggestions.
>
>
> I’m not really trying to advocate for “copyOf”.  I think we should really
> have something more concise in a case like this.  My main point is that
> just using `mutating` is inaccurate and therefore probably not the right
> solution.
>
> Your question about passing in an object (I assume you mean a reference
> type here) is a good one.  In an ideal world that would probably not be
> allowed as it doesn’t really make sense to replace the reference during
> reduction.  Unfortunately I don’t think we have a way to prevent that at
> the moment.
>
>
> On Tue, Jan 24, 2017 at 2:43 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>
> It's only verbose if the words aren't needed! The shortest way to describe
> something with sufficient accuracy can never be verbose, let alone
> undesirable, and I highly agree with this concern. We already have names of
> this form, such as `FloatingPoint.init(signOf:magnitudeOf:)`.
>
>
> I mostly agree with this Xiaodi, but I also think that commonly known and
> frequently used methods like `reduce` deserve to be as concise as
> possible.  That is less a concern with less common and less frequently used
> signatures.
>
>
> On Tue, Jan 24, 2017 at 07:33 Matthew Johnson via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
>
> Sent from my iPad
>
> On Jan 24, 2017, at 1:54 AM, Chris Eidhof via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I've thought about it for a few days, and really like
> `reduce(mutating:_)`.
>
>
> I'm not a fan of this.  It reads in a way that makes it seem like the
> parameter should be inout, but it isn't.  A variation of reduce where the
> initial value parameter *is* inout is perfectly sensible (whether or not we
> want it in the standard library).  With that in mind, I don't think we
> should use this name.
>
> Unfortunately I don't have a better suggestion.  I think it was Brent who
> suggested "mutatingCopyOf" which is more accurate, but also undesirably
> verbose.
>
> I've updated the PR, and am now happy for this to go into review.
>
> https://github.com/apple/swift-evolution/pull/587
>
> On Mon, Jan 23, 2017 at 8:27 AM, Russ Bishop <xenadu at gmail.com> wrote:
>
>
> On Jan 22, 2017, at 10:56 PM, Chris Eidhof <chris at eidhof.nl> wrote:
>
> Not as a direct reply to Russ, but just to reiterate: to me, there are two
> clear benefits of using the `inout` version of reduce:
>
> 1. The performance (currently discussed at length)
> 2. Readability (because we can use mutating methods on `inout` arguments).
>
> Even if the compiler were to optimize the unnecessary copy of `return arr
> + [el]` away, there are still a lot of other mutable methods that you might
> want to use within the reduce closure. So I think the proposal is still
> very valid even if the compiler optimizations would magically appear
> tomorrow.
>
> To push this proposal forward a little bit, I'd like to come up with a
> good name. It seems like we shouldn't overload `reduce`, but choose a
> different name, so that we don't stress the typechecker. Any other
> suggestions?
>
> On Mon, Jan 23, 2017 at 7:11 AM, Russ Bishop <xenadu at gmail.com> wrote:
> --
> Chris Eidhof
>
>
>
> Sorry for the derail!
>
> reduce(mutating:_:) { } is still my favorite; You can take mutating to
> mean we will copy the value now but mutate it later.
>
>
> Some alternatives:
>
> reduce(forMutating:_:) { }
>
> reduce(forInout:_:) { }
>
> reduce(initial:_:) { }
>
> reduce(copying:mutate:) { }
>
> // just kidding...
> reduce(copyForLaterMutating:_:) { }
>
>
>
> It should definitely be some form of reduce.
>
> Russ
>
>
>
>
> --
> Chris Eidhof
>
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>
>
> --
> Chris Eidhof
>
>
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