[swift-evolution] Reduce with inout

[Florent Bruneau]

Hi,

Looks like there is a typo in the proposal:

    func reduce<A>(mutating: A, _ combine: (inout A, Iterator.Element) -> ()) -> A {
        var result = initial

This makes use of `initial` that is not defined, should be:

    func reduce<A>(mutating initial: A, _ combine: (inout A, Iterator.Element) -> ()) -> A {
        var result = initial

> Le 24 janv. 2017 à 08:54, Chris Eidhof via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> I've thought about it for a few days, and really like `reduce(mutating:_)`. 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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