Why? > Le 4 mai 2017 à 19:14, Robert Widmann via swift-evolution > <[email protected]> a écrit : > > 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 > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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