A plain, simple, but very deep THANK YOU! Gwendal Roué
> Le 20 juin 2017 à 01:40, Douglas Gregor via swift-evolution > <swift-evolution@swift.org> a écrit : > > 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
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