Hi, I am sorry if this was already considered (jumping in a bit late), but what about using the following syntax:
let fn = aGameView.insertSubview(_, aboveSubview: _) This is similar to a function calling syntax (rather than function definition syntax), but with _ instead of specific arguments. The reason I think this may be useful is because it could be generalized to a syntax for partial application (assuming such functionality is desired in Swift): let insertCardViewAtTheBottomOfTheDeck = aGameView.insertSubview(_, aboveSubview: playingSurfaceView) then: insertCardViewAtTheBottomOfTheDeck(anotherCard) Or: let insertMyCard = aGameView.insertSubview(myCard, aboveSubview: _) then: insertMyCard(aboveSubview:otherCard) In the above examples, the definitions of insertCardViewAtTheBottomOfTheDeck and insertMyCard would return partially applied functions. Whereas the first example, the definition of fn, where all arguments are specified as _ is a special case that refers to the original function. Some of the issues mentioned in the proposal remain, for example, how to disambiguate same function names with different parameter types, such as: let fn1 = aGameView.insertSubview(_, aboveSubview: _:CardView) or let fn2 = aGameView.insertSubview(_, aboveSubview: _ as CardView) Or different return values: let fn3 = aGameView.insertSubview(_, aboveSubview: playingSurfaceView) -> Bool Getters and setters, using the example from the proposal: let getRow = someMatrix.subscript(row: _).get All of the above assumes, of course, that presence of one or more _ is sufficient to parse these not as function calls, but partial application expressions (with the special case of all _s being just reference to the original function). If that’s the case, it would eliminate the need for back-ticks. Regards, Bart > On Dec 27, 2015, at 02:22, Douglas Gregor via swift-evolution > <swift-evolution@swift.org> 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:)` > 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]) > -> () > If we introduce property behaviors into Swift, the back-tick syntax could > also be used to refer to behaviors, e.g., accessing the lazy behavior of a > property: > > self.`myProperty.lazy`.clear() > Base names that are meaningful keywords (init and subscript) can be escaped > with a nested pair of back-ticks: > > extension Font { > func `subscript`() -> Font { > // return the subscript version of the given font > } > } > > let getSubscript = font.``subscript`()` // has type () -> Font > The "produce the Objective-C selector for the given method" operation will be > the subject of a separate proposal. However, here is one possibility that > illustrations how it uses the proposed syntax here: > > let getter: Selector = objc_selector(NSDictionary.`subscript(_:).get`) // > produces objectForKeyedSubscript: > let setter: Selector = objc_selector(NSDictionary.`subscript(_:).set`) // > produces setObject:forKeyedSubscript: > > <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#impact-on-existing-code>Impact > on existing code > > This is a purely additive feature that has no impact on existing code. The > syntactic space it uses is already present, and it merely extends the use of > back-ticks from storing a single identifier to more complex names. > > > <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered>Alternatives > considered > > Michael Henson proposed > <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html> > naming getters and setters using # syntax followed by get or set, e.g., > > let specificTitle = button.currentTitle#get > The use of postfix # is a reasonable alternative here, and more lightweight > than two back-ticks for the simple getter/setter case. The notion could be > extended to allow argument labels for functions, discussed here > <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002210.html>. > The proposals in that discussion actually included type annotations as well, > but the syntax seems cleaner---and more directly focused on names---without > them, e.g.,: > > let fn = someView.insertSubview#(_:at:) > which works. I didn't go with this syntax because (1) it breaks up Swift > method names such as insertSubview(_:at:)with an # in the middle, and (2) > while useful, this feature doesn't seem important enough to justify > overloading #further. > > Joe Groff notes > <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/003008.html> > that lenses are a better solution than manually retrieving getter/setter > functions when the intent is to actually operate on the properties. That > weakens the case this proposal makes for making getters/setters available as > functions. However, it doesn't address the general naming issue or the desire > to retrieve the Objective-C selector for a getter/setter. > > 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? > > > - Doug > > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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