[swift-evolution] Reduce with inout

Jonathan Hull jhull at gbis.com
Wed Jan 25 01:00:49 CST 2017

+1  Best so far.

> On Jan 24, 2017, at 10:36 AM, Pyry Jahkola via swift-evolution <swift-evolution at swift.org> wrote:
> Freak Show wrote:
>> Am I the only one who finds this incredibly ugly and hard to read?
>> This is more or less solved by inject:into: idiom.  There is no reason for inout for this particular problem.
> Yeah, the original signature seems more useful. If you go all `inout` like Gwendal suggested, you might as well just iterate over the sequence with `for x in xs`, updating the state as you go.
> But your comment brought another idea to mind: if `mutating:` is considered a bad name for a non-`inout` argument, how about `reduce(into:combine:)`, similar to what Karl suggested earlier in this thread?
> I think it reads very well at the call site, does not suggest `inout`ness of the argument too much (of course there's no `&` at the call site either), and it's still easily found with auto-completion:
>     let counts = words.reduce(into: [:]) {
>       $0[$1] = ($0[$1] ?? 0) + 1
>     }
> — Pyry
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