[swift-evolution] SE-0171: Reduce with inout

[BJ Homer]

Does inference still work correctly when trailing closure syntax is used, if the arguments are not given types?

For example, here’s some code that works in Swift right now:

let a = [1, 2, 3, 4, 5]
let b = a.reduce([]) { (result, element) in
    return result + [element * 2]
}

Under the new proposal, this code would also be valid:

let a = [1, 2, 3, 4, 5]

let b = a.reduce([]) { (result, element) in
    result.append(element * 2)
}
Note that these both of these closures appear to have the same signature: two parameters of inferred type, and an inferred return type. The “inout” and return types differ, but neither are specified here. Will the compiler be able to correctly infer the types based on the presence or absence of a “return” statement in the closure body? If not, it seems like the first example will become ambiguous.

-BJ


> On Apr 14, 2017, at 12:37 PM, Ben Cohen via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
> Hello Swift community,
> 
> The review of “SE-0171: Reduce with inout" begins now and runs through the Friday after next, April 14th. The proposal is available here:
> 	https://github.com/apple/swift-evolution/blob/master/proposals/0171-reduce-with-inout.md <https://github.com/apple/swift-evolution/blob/master/proposals/0155-normalize-enum-case-representation.md>
> 
> Reviews are an important part of the Swift evolution process. All reviews should be sent to the swift-evolution mailing list at
> 	https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
> or, if you would like to keep your feedback private, directly to the review manager. When replying, please try to keep the proposal link at the top of the message:
> 
> 	Proposal link: https://github.com/apple/swift-evolution/blob/master/proposals/0171-reduce-with-inout.md <https://github.com/apple/swift-evolution/blob/master/proposals/0155-normalize-enum-case-representation.md>
> 
> 	Reply text
> 
> 	Other replies
> 
> What goes into a review?
> 
> The goal of the review process is to improve the proposal under review through constructive criticism and, eventually, determine the direction of Swift. When writing your review, here are some questions you might want to answer in your review:
> 
> 	• What is your evaluation of the proposal?
> 	• Is the problem being addressed significant enough to warrant a change to Swift?
> 	• Does this proposal fit well with the feel and direction of Swift?
> 	• If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
> 	• How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> 
> More information about the Swift evolution process is available at https://github.com/apple/swift-evolution/blob/master/process.md <https://github.com/apple/swift-evolution/blob/master/process.md>
> 
> Thank you,
> 
> Ben Cohen
> Review Manager
> 
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
> https://lists.swift.org/mailman/listinfo/swift-evolution

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20170414/a19de916/attachment.html>