> On Dec 27, 2015, at 1:32 PM, Joe Groff via swift-evolution > <[email protected]> wrote: > > 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.
At first glance it seems like we can remove the parens altogether if we went with this approach. Could instance.`foo:bar:` work (instance.`foo` in the no-arg case)? I’m not sure how removing parens would work for inits and subscripts though. > - 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] <mailto:[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> > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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