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

Thu May 4 23:47:46 CDT 2017

Now I'm confused. The ordinary meaning of the word "shuffle" is not
changing but rather reordering, and all of your examples are of reordering.

To be clear, are you proposing the prohibition of *adding or removing*
labels as well? A previous discussion on tuple shuffling on this list saw
consensus that assigning a value of type (label1: T, label2: U) to a
variable of type (T, U) and vice versa should absolutely be supported,
whether or not reordering is permitted.

And how about *restating* existing labels without any adding or removing?
To be clear:

```
let (partialValue: v, overflow: o) = 42.addingReportingOverflow(42)
```

...involves absolutely no changes in labels whatsoever. The return type is
(partialValue: Int, overflow: ArithmeticOverflow).

Either one of these scenarios is commonly used, and it is astonishing to me
that they would be eliminated.

On Thu, May 4, 2017 at 23:28 Robert Widmann <devteam.codafi at gmail.com>
wrote:

> That doesn't involve a parameter *reordering*, but because it changes
> argument labels it's a shuffle.
>
> ~Robert Widmann
>
> 2017/05/05 0:16、Xiaodi Wu <xiaodi.wu at gmail.com> のメッセージ:
>
> Robert,
>
> As I mentioned on Twitter, getting rid of tuple shuffles would not cure
> your example, which does not involve a shuffle. Unless you're proposing to
> disallow the use of labels during destructuring entirely, which I would
> think to be very much unacceptable. Example:
>
> ```
> let (partialValue: v, overflow: o) = 42.addingReportingOverflow(42)
> ```
>
> This involves no shuffling and should absolutely remain allowed.
>
>
> On Thu, May 4, 2017 at 21:15 Robert Widmann via swift-evolution <
> 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 = 5var y = 10var 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
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>
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