[swift-evolution] Reduce with inout

[Xiaodi Wu]

A serious possibility would be: `reduce(mutableCopyOf: x) { ... }`.

It's verbose, but the nicer-looking `reduce(mutating: x) { ... }` is
incorrect since, as Charles pointed out to Dave, it's not `x` that's
mutated but rather a mutable copy of it, so it doesn't matter if `x` itself
is declared with `let` or `var`.


On Tue, Jan 17, 2017 at 7:46 PM, Sean Heber <sean at fifthace.com> wrote:

> `reuse`
>
> Then we just need an excuse for a function named ‘recycle’...
>
> l8r
> Sean
>
>
> > On Jan 17, 2017, at 7:36 PM, T.J. Usiyan via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > `reduceInout`
> >
> > On Tue, Jan 17, 2017 at 6:30 PM, Xiaodi Wu via swift-evolution <
> swift-evolution at swift.org> wrote:
> > Agree. The functional style should keep the functional name.
> >
> > On Tue, Jan 17, 2017 at 16:18 David Sweeris via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > On Jan 17, 2017, at 16:11, Karl Wagner via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> >>
> >>> On 17 Jan 2017, at 23:09, Karl Wagner <karl.swift at springsup.com>
> wrote:
> >>>
> >>>
> >>>> On 16 Jan 2017, at 14:49, Chris Eidhof via swift-evolution <
> swift-evolution at swift.org> wrote:
> >>>>
> >>>> Hi,
> >>>>
> >>>> How does everyone feel about adding a second version of `reduce` to
> `Sequence`? Instead of a `combine` function that's of type `(A, Element) ->
> A`, it would be `(inout A, Element) -> ()`. This way, we can write nice
> functionals algorithms, but have the benefits of inout (mutation within the
> function, and hopefully some copy eliminations).
> >>>>
> >>>> IIRC, Loïc Lecrenier first asked this on Twitter. I've been using it
> ever since, because it can really improve readability (the possible
> performance gain is nice, too).
> >>>>
> >>>> Here's `reduce` with an `inout` parameter, including a sample:
> https://gist.github.com/chriseidhof/fd3e9aa621569752d1b04230f92969d7
> >>>>
> >>>> --
> >>>> Chris Eidhof
> >>>> _______________________________________________
> >>>> swift-evolution mailing list
> >>>> swift-evolution at swift.org
> >>>> https://lists.swift.org/mailman/listinfo/swift-evolution
> >>>
> >>> +1
> >>>
> >>> I would even argue for it to be the default.
> >>
> >> I mean, assuming having two “reduce”s would stress the typechecker, as
> Joe suggested it might, I would say “inout” makes sense to be the default
> and the other one can find itself a new name.
> >
> > IIRC, the "reduce" name comes from functional programming... should the
> functional style keep the functional name?
> >
> > - Dave Sweeris
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> >
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> >
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>
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