[swift-evolution] [Proposal][Discussion] Deprecate Tuple Shuffles

Fri May 5 10:34:06 CDT 2017

On 05.05.2017 6:12, Jose Cheyo Jimenez via swift-evolution wrote:
> I can't think of a single time when I would need a tuple shuffle but I don't really 
> work with tuples much. It would be great to hear other people's usage of this feature.
> 
> I did not know that types could be overloaded with values. That was very surprising 
> to me. Honestly I think that is the issue here. Not sure what can be done about it.
> 

> let Int = 5 // works
> let Void = "what?" // works.

Very interesting. Could some one clarify, why this is allowed? Isn't this is a bug we 
want to fix? At least by requiring a tilda like `Int`
And of course, you can't "overload" user defined type:
struct S {}
let S = 10 // Error: invalid redeclaration of 'S'

> 
> 
> On May 4, 2017, at 7:14 PM, Robert Widmann via swift-evolution 
> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> Hi all,
>>
>> So sorry that this proposal comes so late in the game, but I feel it’s too 
>> important not to bring it to the attention of the community now.  Attached is a 
>> proposal to deprecate a language feature many of you will probably have never had 
>> the chance to use: Tuple Shuffles.  I’ve attached a copy of the first draft of the 
>> proposal below, but the latest copy can be read on Github 
>> <https://github.com/apple/swift-evolution/pull/705/files>.
>>
>> Thanks!
>>
>> ~Robert Widmann
>>
>>
>>   Deprecate Tuple Shuffles
>>
>>   * Proposal: SE-NNNN
>>     <https://github.com/CodaFi/swift-evolution/blob/8eaf320b3c2a117909fc0269c398e89c033a4b9f/proposals/NNNN-filename.md>
>>   * Authors: Robert Widmann <https://github.com/codafi>
>>   * Review Manager: TBD
>>   * Status: Awaiting review
>>
>>
>>     <https://github.com/CodaFi/swift-evolution/blob/8eaf320b3c2a117909fc0269c398e89c033a4b9f/proposals/NNNN-deprecate-tuple-shuffles.md#introduction>Introduction
>>
>> This proposal seeks the deprecation of a little-known feature of Swift called a 
>> "Tuple Shuffle".
>>
>>
>>     <https://github.com/CodaFi/swift-evolution/blob/8eaf320b3c2a117909fc0269c398e89c033a4b9f/proposals/NNNN-deprecate-tuple-shuffles.md#motivation>Motivation
>>
>> A tuple-shuffle is an undocumented feature of Swift in which one can re-order the 
>> indices of a tuple by writing a pattern that describes a permutation in a syntax 
>> reminiscent of adding type-annotations to a parameter list:
>>
>> let  a=  (x:1,y:2)
>> var  b:  (y:Int,x:Int)
>> b=  a
>>
>> It can be used to simultaneously destructure and reorder a tuple:
>>
>> let  tuple=  (first:0,second: (x:1,y:2))
>> let  (second: (x: b,y: c),first: a)=  tuple
>>
>> It can also be used to map parameter labels out of order in a call expression:
>>
>> func  foo(_  : (x :Int, y :Int)) {}
>> foo((y:5,x:10))// Valid
>>
>> Note that a tuple shuffle is distinct from a re-assignment through a tuple pattern. 
>> For example, this series of statements will continue to function as before:
>>
>> var  x=  5
>> var  y=  10
>> var  z=  15
>> (z, y, x)=  (x, z, y)
>>
>> Their inclusion in the language complicates every part of the compiler stack, uses 
>> a syntax that can be confused for type annotations 
>> <https://twitter.com/CodaFi_/status/860246169854894081>, contradicts the goals of 
>> earlier SE's (see SE-0060 
>> <https://github.com/apple/swift-evolution/blob/9cf2685293108ea3efcbebb7ee6a8618b83d4a90/proposals/0060-defaulted-parameter-order.md>), 
>> and makes non-sensical patterns possible in surprising places.
>>
>> Take switch-statements, for example:
>>
>> switch  ((0,0),0){
>> case  (_  :let  (y, z),_  :let  s):  ()// We are forbidden from giving these patterns names other than "_"
>> default:  ()
>> }
>>
>> This proposal seeks to deprecate them in Swift 3 compatibility mode and enforce 
>> that deprecation as a hard error in Swift 4 to facilitate their eventual removal 
>> from the language.
>>
>>
>>     <https://github.com/CodaFi/swift-evolution/blob/8eaf320b3c2a117909fc0269c398e89c033a4b9f/proposals/NNNN-deprecate-tuple-shuffles.md#proposed-solution>Proposed
>>     solution
>>
>> Construction of Tuple Shuffle Expressions will become a warning in Swift 3 
>> compatibility mode and will be a hard-error in Swift 4.
>>
>>
>>     <https://github.com/CodaFi/swift-evolution/blob/8eaf320b3c2a117909fc0269c398e89c033a4b9f/proposals/NNNN-deprecate-tuple-shuffles.md#detailed-design>Detailed
>>     design
>>
>> In addition to the necessary diagnostics, the grammar will be ammended to simplify 
>> the following productions:
>>
>> tuple-pattern → (tuple-pattern-element-list <opt>)
>> tuple-pattern-element-list → tuple-pattern-element | tuple-pattern-element , tuple-pattern-element-list
>> - tuple-pattern-element → pattern | identifier:pattern
>> + tuple-pattern-element → pattern
>>
>>
>>     <https://github.com/CodaFi/swift-evolution/blob/8eaf320b3c2a117909fc0269c398e89c033a4b9f/proposals/NNNN-deprecate-tuple-shuffles.md#impact-on-existing-code>Impact
>>     on Existing Code
>>
>> Because very little code is intentionally using Tuple Shuffles, impact on existing 
>> code will be negligible but not non-zero.
>>
>>
>>     <https://github.com/CodaFi/swift-evolution/blob/8eaf320b3c2a117909fc0269c398e89c033a4b9f/proposals/NNNN-deprecate-tuple-shuffles.md#alternatives-considered>Alternatives
>>     considered
>>
>> Continue to keep the architecture in place to facilitate this feature.
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-evolution
> 
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
> 