[swift-evolution] Reduce with inout

[Karl Wagner]

> 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 <mailto: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 <https://gist.github.com/chriseidhof/fd3e9aa621569752d1b04230f92969d7>
>> 
>> -- 
>> Chris Eidhof
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> 
> +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. 
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