On Tue, 20 Jun 2017 at 01:41, Douglas Gregor via swift-evolution < swift-evolution@swift.org> wrote:
> Hello Swift community, > > Swift 3’s SE-0110 > <https://github.com/apple/swift-evolution/blob/master/proposals/0110-distingish-single-tuple-arg.md> > eliminated > the equivalence between function types that accept a single type and > function types that take multiple arguments. However, for various > implementation > reasons > <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170612/037560.html>, > the implementation of SE-0110 (as well as the elimination of tuple “splat” > behavior in SE-0029 > <https://github.com/apple/swift-evolution/blob/master/proposals/0029-remove-implicit-tuple-splat.md>) > was not fully completed. > > Swift 4 implemented more of SE-0110, which caused a fairly serious > usability regression, particularly with closures. Here are a few simple > examples involving closures that worked in Swift 3 but do not work in Swift > 4: > > // #1: Works in Swift 3, error in Swift 4 > myDictionary.forEach { > print("\($0) -> \($1)") > } > > // #2: Works in Swift 3, error in Swift 4 > myDictionary.forEach { key, value in > print("\(key) -> \(value)") > } > > // #3: Works in Swift 3, error in Swift 4 > myDictionary.forEach { (key, value) in > print("\(key) -> \(value)") > } > > > Similar issues occur with passing multi-argument functions where a tuple > argument is expected: > > // #4: Works in Swift 3, error in Swift 4 > _ = zip(array1, array2).map(+) > > > In all of these cases, it is possible to write a closure that achieves the > desired effect, but the result is more verbose and less intuitive: > > // Works in both Swift 3 and Swift 4 > myDictionary.forEach { element in > let (key, value) = element > print("\(key) -> \(value)") > } > > > The Swift core team feels that these usability regressions are > unacceptable for Swift 4. There are a number of promising solutions that > would provide a better model for closures and address the usability > regression, but fully designing and implementing those are out of scope for > Swift 4. Therefore, we will “back out” the SE-0110 change regarding > function arguments from Swift 4. > > Specifically, when passing an argument value of function type (including > closures) to a parameter of function type, a multi-parameter argument > function can be passed to a parameter whose function type accepts a single > tuple (whose tuple elements match the parameter types of the argument > function). Practically speaking, all of the examples #1-#4 will be accepted > in both Swift 3 and Swift 4. > > We will revisit the design in this area post-Swift 4. > > - Doug > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution > Thank you :) -- Víctor Pimentel -- D I G I T A L T E L C O E X P E R I E N C E *[image: Imágenes integradas 5]* *Víctor Pimentel Rodríguez · *Principal iOS Engineer vpimen...@tuenti.com +34 914 294 039 <javascript:void(0);> — +34 687 840 886 <javascript:void(0);> C/ Gran Vía, nº 28, 6ª planta — 28013 Madrid Tuenti Technologies, S.L. www.tu.com www.tuenti.com
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