[swift-evolution] [Review] SE-0066: Standardize function type argument syntax to require parentheses

Tyler Fleming Cloutier cloutiertyler at aol.com
Thu Apr 28 01:41:13 CDT 2016

I’m going to play Devil’s advocate here and ask why not just pull out the parens for function types?

Int, Int -> Int // Two argument function type
(Int, Int) -> Int // Single tuple argument function type


(Int, Int) -> Int // Two argument function type
((Int, Int)) -> Int // Single tuple argument function type

I’ll admit that

let x: Int, Int -> Int 

looks okay, but 

let x: arg1: Int, arg2: Int -> Int

does not look great compared to

let x: (arg1: Int, arg2: Int) -> Int

However, I don’t think it’s an inconsistent rule to require parenthesis when argument labels are specified. Indeed, this behavior is perfectly consistent with current closure syntax.  e.g. { x, y -> Int in /* code */ }

Named tuples would be:

let x: ((arg1: Int, arg2: Int)) -> Int

Which has the double parens, but this is a more infrequent situation.


> On Apr 25, 2016, at 9:22 PM, Douglas Gregor via swift-evolution <swift-evolution at swift.org> wrote:
> Hello Swift community,
> The review of SE-0066 "Standardize function type argument syntax to require parentheses" begins now and runs through May 2, 2016. The proposal is available here:
> https://github.com/apple/swift-evolution/blob/master/proposals/0066-standardize-function-type-syntax.md <https://github.com/apple/swift-evolution/blob/master/proposals/0066-standardize-function-type-syntax.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/0066-standardize-function-type-syntax.md <https://github.com/apple/swift-evolution/blob/master/proposals/0066-standardize-function-type-syntax.md>
> Reply text
> Other replies
>  <https://github.com/apple/swift-evolution#what-goes-into-a-review-1>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?
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> 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,
> Doug Gregor
> Review Manager
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