Some more things to consider: - Our naming conventions encourage the first parameter to most methods to be unlabeled, so unlabeled parameters come up a lot. I don't think there's a grammatical requirement for an identifier before each colon; maybe we can leave out the underscore and use `foo(:bar:)` instead of `foo(_:bar:)` to refer to unlabeled arguments.
- How do labeled references interact with default and variadic arguments? If you have a func foo(x: Int = 0, y: String = 0), can you refer to foo(x:) and foo(y:) to apply some of the defaulted arguments, or only foo(x:y:)? Would foo(y:x:) also work? -Joe > On Dec 27, 2015, at 10:37 AM, Joe Groff via swift-evolution > <[email protected]> wrote: > >> >> On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution >> <[email protected] <mailto:[email protected]>> wrote: >> >> Hi all, >> >> Here’s a proposal draft to allow one to name any function in Swift. In >> effect, it’s continuing the discussion of retrieving getters and setters as >> functions started by Michael Henson here: >> >> >> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html >> >> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html> >> >> the proposal follows, and is available here as well: >> >> >> https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md >> >> <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md> >> >> Comments appreciated! >> >> Generalized Naming for Any Function >> >> Proposal: SE-NNNN >> <https://github.com/apple/swift-evolution/blob/master/proposals/0000-generalized-naming.md> >> Author(s): Doug Gregor <https://github.com/DougGregor> >> Status: Awaiting Review >> Review manager: TBD >> >> <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#introduction>Introduction >> >> Swift includes support for first-class functions, such that any function (or >> method) can be placed into a value of function type. However, it is not >> possible to specifically name every function that is part of a Swift >> program---one cannot provide the argument labels when naming a function, nor >> are property and subscript getters and setters referenceable. This proposal >> introduces a general syntax that allows one to name anything that is a >> function within Swift in an extensible manner. >> >> Swift-evolution thread: Michael Henson started a thread about the >> getter/setter issue here >> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html>, >> continued here >> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002203.html>. >> See the Alternatives considered >> <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered> >> section for commentary on that discussion. >> >> >> <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#motivation>Motivation >> >> It's fairly common in Swift for multiple functions or methods to have the >> same "base name", but be distinguished by parameter labels. For example, >> UIView has three methods with the same base name insertSubview: >> >> extension UIView { >> func insertSubview(view: UIView, at index: Int) >> func insertSubview(view: UIView, aboveSubview siblingSubview: UIView) >> func insertSubview(view: UIView, belowSubview siblingSubview: UIView) >> } >> When calling these methods, the argument labels distinguish the different >> methods, e.g., >> >> someView.insertSubview(view, at: 3) >> someView.insertSubview(view, aboveSubview: otherView) >> someView.insertSubview(view, belowSubview: otherView) >> However, when referencing the function to create a function value, one >> cannot provide the labels: >> >> let fn = someView.insertSubview // ambiguous: could be any of the three >> methods >> In some cases, it is possible to use type annotations to disambiguate: >> >> let fn: (UIView, Int) = someView.insertSubview // ok: uses >> insertSubview(_:at:) >> let fn: (UIView, UIView) = someView.insertSubview // error: still ambiguous! >> To resolve the latter case, one must fall back to creating a closure: >> >> let fn: (UIView, UIView) = { view, otherView in >> button.insertSubview(view, otherView) >> } >> which is painfully tedious. A similar workaround is required to produce a >> function value for a getter of a property, e.g., >> >> extension UIButton { >> var currentTitle: String? { ... } >> } >> >> var fn: () -> String? = { () in >> return button.currentTitle >> } >> One additional bit of motivation: Swift should probably get some way to ask >> for the Objective-C selector for a given method (rather than writing a >> string literal). The argument to such an operation would likely be a >> reference to a method, which would benefit from being able to name any >> method, including getters and setters. >> >> >> <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#proposed-solution>Proposed >> solution >> >> Swift currently has a back-tick escaping syntax that lets one use keywords >> for names, which would otherwise fail to parse. For example, >> >> func `try`() -> Bool { ... } >> declares a function named try, even though try is a keyword. I propose to >> extend the back-tick syntax to allow compound Swift names (e.g., >> insertSubview(_:aboveSubview:)) and references to the accessors of >> properties (e.g., the getter for currentTitle). Specifically, >> >> Compound names can be written entirely within the back-ticks, e.g., >> >> let fn = someView.`insertSubview(_:at:)` >> let fn1 = someView.`insertSubview(_:aboveSubview:)` >> The same syntax can also refer to initializers, e.g., >> >> let buttonFactory = UIButton.`init(type:)` > This part seems reasonable to me. >> Getters and setters can be written using dotted syntax within the back-ticks: >> >> let specificTitle = button.`currentTitle.get` // has type () -> String? >> let otherTitle = UIButton.`currentTitle.get` // has type (UIButton) -> () >> -> String? >> let setTintColor = button.`tintColor.set` // has type (UIColor!) -> () >> The same syntax works with subscript getters and setters as well, using the >> full name of the subscript: >> >> extension Matrix { >> subscript (row row: Int) -> [Double] { >> get { ... } >> set { ... } >> } >> } >> >> let getRow = someMatrix.`subscript(row:).get` // has type (Int) -> () -> >> [Double] >> let setRow = someMatrix.`subscript(row:).set` // has type (Int) -> >> ([Double]) -> () > At least as far as pure Swift is concerned, for unapplied access, like > `UIButton.currentTitle`, I think it would be more consistent with the way > method references works for that to give you the getter (or lens) without > decoration. instance.instanceMethod has type Args -> Ret, and > Type.instanceMethod has type Self -> Args -> Ret; by analogy, since > instance.instanceProperty has type Ret or inout Ret, it's reasonable to > expect Type.instanceProperty to have type Self -> [inout] Ret. Forming a > getter or setter partially applied to an instance feels unmotivated to me—{ > button.currentTitle } or { button.currentTitle = $0 } already work, and are > arguably clearer than this syntax. > > I acknowledge that this leaves forming selectors from setters out to dry, but > I feel like that's something that could be incorporated into a "lens" design > along with typed selectors. As a rough sketch, we could say that the > representation of @convention(selector) T -> inout U is a pair of > getter/setter selectors, and provide API on Selector to grab the individual > selectors from that, maybe Selector(getterFor: > UIView.currentTitle)/(setterFor: UIView.currentTitle). I don't think get/set > is a good interface for working with Swift properties, so I don't like the > idea of building in language support to codify it beyond what's needed for > ObjC interaction. >> Can we drop the back-ticks? It's very tempting to want to drop the >> back-ticks entirely, because something like >> >> let fn = someView.insertSubview(_:at:) >> can be correctly parsed as a reference to insertSubview(_:at:). However, it >> breaks down at the margins, e.g., with getter/setter references or >> no-argument functions: >> >> extension Optional { >> func get() -> T { return self! } >> } >> >> let fn1 = button.currentTitle.get // getter or Optional<String>.get? >> let fn2 = set.removeAllElements() // call or reference? > From what I remember, the bigger concern with allowing foo(bar:bas:) without > backticks is parser error recovery. The unambiguity with call syntax depends > on having the `:)` token pair at the end. The edit distance between > foo(bar:bas:) and a call foo(bar: bas) or work-in-progress call foo(bar: x, > bas: ) is pretty slight, and would be tricky to give good diagnostics for. If > we felt confident we could give good diagnostics, I'd support removing the > backticks. > > -Joe > > _______________________________________________ > swift-evolution mailing list > [email protected] <mailto:[email protected]> > https://lists.swift.org/mailman/listinfo/swift-evolution > <https://lists.swift.org/mailman/listinfo/swift-evolution>
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