[Proposal draft] Generalized Naming for Any Function

[migi (Alex Migicovsky)]

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.

···

On Dec 27, 2015, at 1:32 PM, Joe Groff via swift-evolution <swift-evolution@swift.org> wrote:

- 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 <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto: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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  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&gt;
Author(s): Doug Gregor <https://github.com/DougGregor&gt;
Status: Awaiting Review
Review manager: TBD
<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#introduction&gt;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&gt;, continued here <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002203.html&gt;\. See the Alternatives considered <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered&gt; section for commentary on that discussion.

<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#motivation&gt;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&gt;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

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[Joe_Groff]

Vaguely, I think it could look something like this. You could define a lens function by having it return `inout`. Calling the function produces an lvalue whose access nests within the accesses of its input `inout` parameters, if any, allowing for things like:

var localVar = 1
let localRef: () -> inout Int = { &localVar }

func second(inout array: [Int]) -> inout Int {
  return &array[1]
}

// Maybe you can define an inout function with accessors too
func fahrenheit(inout celsius: Double) -> inout Double {
  get {
    return celsius * 9/5 + 32
  }
  set {
    celsius = (newValue - 32) * 5/9
  }
}

and you could access the unapplied lens for an instance property using `Type.property` syntax, analogous to how `Type.method` works. I feel like if we did that, then it would obviate the need for explicit `property.get` or `property.set` for most native Swift uses, though maybe not ObjC interop uses.

-Joe

···

On Dec 27, 2015, at 2:47 PM, John McCall <rjmccall@apple.com> wrote:

On Dec 27, 2015, at 10:37 AM, Joe Groff via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

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.

I know this might be too early, but: what syntax are we thinking of for lenses? We might want to design this with future consistency in mind.

[Douglas_Gregor]

Sent from my iPhone

We also have a problem with disambiguating same-named members that come from different extensions, whether via protocol extensions or independent concrete extensions from different modules. Could we extend this scheme to allow for disambiguating extension methods by protocol/module name?

That's a fantastic idea!

It does introduce some ambiguities at the margins. Given

  foo.`bar.get`()

Do we look for bar in the lexical scope or in the member scope of foo? Or both with yet another disambiguation mechanism?

I'm still traumatized by implementing the related C++ rules for

  foo.bar::get

:)

This is the other thing that nudges me toward dropping getters/setters from the generalized naming proposal, because it leaves the use of '.' within backticks for your newly-proposed meaning.

···

Sent from my iPhone

On Dec 29, 2015, at 11:03 AM, Douglas Gregor via swift-evolution <swift-evolution@swift.org> wrote:

On Dec 29, 2015, at 10:17 AM, Joe Groff <jgroff@apple.com> wrote:

extension ProtocolA { func foo() }
extension ProtocolB { func foo() }

public struct Foo: ProtocolA, ProtocolB {
  func callBothFoos() {
    self.`ProtocolA.foo`()
    self.`ProtocolB.foo`()
  }
}

import A // extends Bar with bar()
import B // also extends Bar with bar()

extension Bar {
  func callBothBars() {
    self.`A.bar`()
    self.`B.bar`()
  }
}

-Joe

On Dec 26, 2015, at 11:22 PM, 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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md

Comments appreciated!

Generalized Naming for Any Function
Proposal: SE-NNNN
Author(s): Doug Gregor
Status: Awaiting Review
Review manager: TBD
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, continued here. See the Alternatives considered section for commentary on that discussion.

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.

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:
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.

Alternatives considered

Michael Henson proposed 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. 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 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

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https://lists.swift.org/mailman/listinfo/swift-evolution

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[Erica_Sadun]

Talk about things you didn't know you needed until you see them. This is a really nice way of disambiguating!

-- E

···

On Dec 29, 2015, at 12:03 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org> wrote:

Sent from my iPhone

On Dec 29, 2015, at 10:17 AM, Joe Groff <jgroff@apple.com <mailto:jgroff@apple.com>> wrote:

We also have a problem with disambiguating same-named members that come from different extensions, whether via protocol extensions or independent concrete extensions from different modules. Could we extend this scheme to allow for disambiguating extension methods by protocol/module name?

That's a fantastic idea!

extension ProtocolA { func foo() }
extension ProtocolB { func foo() }

public struct Foo: ProtocolA, ProtocolB {
  func callBothFoos() {
    self.`ProtocolA.foo`()
    self.`ProtocolB.foo`()
  }
}

import A // extends Bar with bar()
import B // also extends Bar with bar()

extension Bar {
  func callBothBars() {
    self.`A.bar`()
    self.`B.bar`()
  }
}

-Joe

On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto: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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  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&gt;
Author(s): Doug Gregor <https://github.com/DougGregor&gt;
Status: Awaiting Review
Review manager: TBD
<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#introduction&gt;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&gt;, continued here <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002203.html&gt;\. See the Alternatives considered <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered&gt; section for commentary on that discussion.

<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#motivation&gt;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&gt;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&gt;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&gt;Alternatives considered

Michael Henson proposed <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html&gt; 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&gt;\. 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&gt; 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

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[Chris_Lattner]

If you were to go that far, I’d suggest looking at this as a different version of the “." operator. If you resyntax curried to something else like (just a strawman, intentionally ugly syntax):

  foo.#bar

Then you’d get a nice property that the plain old dot operator always has to be fully applied. This certainly would be a win for error recovery. Also, if you did this, you wouldn’t need the backticks from doug’s proposal either for things like:

  foo.#bar(param1:param2:)

either.

-Chris

···

On Dec 27, 2015, at 4:09 PM, John McCall <rjmccall@apple.com> wrote:

I’m a fan of good error recovery, but I don’t think it is a major concern here for two reasons:

1) The most common case in a method will lack a label, and "thing.foo(_: “ and “thing.foo(:” are both unambiguously a curried reference.
2) A common case of accidentally completing a nullary call (thing.foo() vs thing.foo) will produce a type error. We already produce good QoI for an unapplied function - adding the inverse would be simple.

Further, it will be uncommon *in general* to form a curried reference, so error recovery doesn’t have to be perfect in all the edge cases. As with other commenters, if it is at all possible to avoid the extra backticks, I’d really prefer that.

The concern, I think, is that a messed-up normal call might look like a curried reference.

My inclination would be to go the other way: if we get a syntax for this that we like, I think we should use it for *all* curried member references, and reject things like foo.bar in favor of foo.`bar`. The ability to write foo.bar for a method has always struck me as more clever than wise, to be honest.

[stephencelis]

While the conventions encourage the first parameter to be unlabeled, it doesn't enforce it (and there are exceptions in the standard library, like `removeAll(keepCapacity:)`, as well as `stride(to:…)` and `stride(through:…)`.

Stephen

···

On Dec 28, 2015, at 11:47 AM, Alex Migicovsky via swift-evolution <swift-evolution@swift.org> wrote:

On Dec 27, 2015, at 1:32 PM, Joe Groff via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> 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.

[Brent_Royal-Gordon]

and you could access the unapplied lens for an instance property using `Type.property` syntax, analogous to how `Type.method` works. I feel like if we did that, then it would obviate the need for explicit `property.get` or `property.set` for most native Swift uses, though maybe not ObjC interop uses.

I feel like if you don't have a way to fetch an unbound getter, you're missing the 90% case, which is constructs like:

  let textValues = textViews.map(.#text.get)

I do agree with you that the setter is usually far less useful—although the ReactiveCocoa people might not agree with us on that.

···

--
Brent Royal-Gordon
Architechies

[dwaite (David Waite)]

Does this bridge over to referencing properties, such as using:

struct Bar {
   var counter:Int = 0
}

let fn3 = Bar#counter.get

-DW

···

On Dec 28, 2015, at 8:05 AM, T.J. Usiyan via swift-evolution <swift-evolution@swift.org> wrote:

Do things get any better if we combine the proposed changes and remove the bare case? Begin function reference with some symbol (# here but it doesn't matter), only use back tics to disambiguate keywords (which lines up with their current use) and remove the unadorned case to avoid ambiguity.

class Foo {
	func doSomething() { }
	func doSomething(value: Int) { }
	func sub
}

let fn = Foo#doSomething // no longer allowed
let fn = Foo#doSomething() // okay
let fn2 = Foo#doSomething(_:) // okay

// and

let getRow = someMatrix#`subscript`(row:).get

On Sun, Dec 27, 2015 at 10:40 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Dec 27, 2015, at 12:27 AM, Frederick Kellison-Linn via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Given that someView.insertSubview(_:at:) can be correctly parsed, I would strongly lean towards the no-backtick alternative mentioned at the end. I feel as though the backticks end up looking very cluttered (particularly when you get into the double-nested backticks), and it seems cleaner to be able to reference a method as it was declared rather than having to add extra syntax.

In reference to the issues noted with this approach:

IMO, there is already enough syntactic difference between getters/setters and normal methods to justify requiring a different syntax to reference them. For instance, the # syntax could be used so that, button.currentTitle.get would reference Optional<String>.get, and button.currentTitle#get would reference the getter. Or, button.`currentTitle.get` could reference the getter (i.e. backticks are only required in cases that are ambiguous).

I also think it is reasonable to require that in the case of a method with no arguments such as set.removeAllElements, the programmer be expected to know the difference between the expression with and without the trailing parenthesis. After all, that distinction already exists in the language, and would not disappear with this proposed addition. If a parallel syntax for referencing methods with no arguments is strongly desired, perhaps something such as set.removeAllElements(:), set#removeAllElements(), or similar could be used, though I think that the present system for referencing these methods is sufficient.

Are there other obvious reasons why this alternative wouldn’t work? I think it is the cleanest of the alternatives and avoids littering the code with backticks.

Not having the back-ticks means that you will need to use contextual type information to disambiguate the zero-parameter case from other cases. For example:

  class Foo {
    func doSomething() { }
    func doSomething(value: Int) { }
  }

  let fn = Foo.doSomething // ambiguous
  let fn2 = Foo.doSomething(_:) // okay
  let fn3: (Foo) -> () -> Void = Foo.doSomething // okay
  let fn3: (Foo) -> (Int) -> Void = Foo.doSomething // okay

My general complaint with the “drop the backticks” approach is that it doesn’t solve the whole problem. Sure, it solves 95% of the problem with a little less syntax, but now you need to invent yet another mechanism to handle the other cases (set, contextual type disambiguation, etc)… which seems inconsistent to me.

  - Doug

On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto: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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  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&gt;
Author(s): Doug Gregor <https://github.com/DougGregor&gt;
Status: Awaiting Review
Review manager: TBD
<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#introduction&gt;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&gt;, continued here <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002203.html&gt;\. See the Alternatives considered <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered&gt; section for commentary on that discussion.

<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#motivation&gt;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&gt;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&gt;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&gt;Alternatives considered

Michael Henson proposed <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html&gt; 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&gt;\. 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&gt; 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

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[trs (Thorsten Seitz)]

Looks good so far.

Top-level functions:

#doSomething()
ModuleName#doSomething() // is it a problem to distinguish modules and classes here?

What about static/class functions? Any idea how to fit them into that scheme?

-Thorsten

···

Am 28.12.2015 um 16:05 schrieb T.J. Usiyan via swift-evolution <swift-evolution@swift.org>:

Do things get any better if we combine the proposed changes and remove the bare case? Begin function reference with some symbol (# here but it doesn't matter), only use back tics to disambiguate keywords (which lines up with their current use) and remove the unadorned case to avoid ambiguity.

class Foo {
	func doSomething() { }
	func doSomething(value: Int) { }
	func sub
}

let fn = Foo#doSomething // no longer allowed
let fn = Foo#doSomething() // okay
let fn2 = Foo#doSomething(_:) // okay

// and

let getRow = someMatrix#`subscript`(row:).get

On Sun, Dec 27, 2015 at 10:40 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org> wrote:

On Dec 27, 2015, at 12:27 AM, Frederick Kellison-Linn via swift-evolution <swift-evolution@swift.org> wrote:

Given that someView.insertSubview(_:at:) can be correctly parsed, I would strongly lean towards the no-backtick alternative mentioned at the end. I feel as though the backticks end up looking very cluttered (particularly when you get into the double-nested backticks), and it seems cleaner to be able to reference a method as it was declared rather than having to add extra syntax.

In reference to the issues noted with this approach:

IMO, there is already enough syntactic difference between getters/setters and normal methods to justify requiring a different syntax to reference them. For instance, the # syntax could be used so that, button.currentTitle.get would reference Optional<String>.get, and button.currentTitle#get would reference the getter. Or, button.`currentTitle.get` could reference the getter (i.e. backticks are only required in cases that are ambiguous).

I also think it is reasonable to require that in the case of a method with no arguments such as set.removeAllElements, the programmer be expected to know the difference between the expression with and without the trailing parenthesis. After all, that distinction already exists in the language, and would not disappear with this proposed addition. If a parallel syntax for referencing methods with no arguments is strongly desired, perhaps something such as set.removeAllElements(:), set#removeAllElements(), or similar could be used, though I think that the present system for referencing these methods is sufficient.

Are there other obvious reasons why this alternative wouldn’t work? I think it is the cleanest of the alternatives and avoids littering the code with backticks.

Not having the back-ticks means that you will need to use contextual type information to disambiguate the zero-parameter case from other cases. For example:

  class Foo {
    func doSomething() { }
    func doSomething(value: Int) { }
  }

  let fn = Foo.doSomething // ambiguous
  let fn2 = Foo.doSomething(_:) // okay
  let fn3: (Foo) -> () -> Void = Foo.doSomething // okay
  let fn3: (Foo) -> (Int) -> Void = Foo.doSomething // okay

My general complaint with the “drop the backticks” approach is that it doesn’t solve the whole problem. Sure, it solves 95% of the problem with a little less syntax, but now you need to invent yet another mechanism to handle the other cases (set, contextual type disambiguation, etc)… which seems inconsistent to me.

  - Doug

On Dec 26, 2015, at 11:22 PM, 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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md

Comments appreciated!

Generalized Naming for Any Function

Proposal: SE-NNNN
Author(s): Doug Gregor
Status: Awaiting Review
Review manager: TBD
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, continued here. See the Alternatives considered section for commentary on that discussion.

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.

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:
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.

Alternatives considered

Michael Henson proposed 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. 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 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

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[Wallacy]

And if we only make the actual type inference more powerful?

Using the examples on proposal:

extension UIView {
  func insertSubview(view: UIView, at index: Int)
  func insertSubview(view: UIView, aboveSubview siblingSubview: UIView)
  func insertSubview(view: UIView, belowSubview siblingSubview: UIView)
}

let fn1: (UIView, Int) = someView.insertSubview // ok: uses
insertSubview(_:at:)let fn2: (UIView, aboveSubview: UIView) =
someView.insertSubview // Ok: no more ambiguous!let fn3: (UIView,
belowSubview: UIView) = someView.insertSubview // Ok: no more
ambiguous!

And for properties:

let specificTitle:() -> String? = button.currentTitle // will pick the
getterlet otherTitle: (UIButton) -> () -> String? =
UIButton.currentTitle // will pick the getterlet setTintColor:
(UIColor!) -> () = button.tintColor // will pick the setter

This can be an opportunity to do something like that:

func processColor(data: Any, delegate : (UIColor!) -> ())

processColor(someData, button.tintColor) // will pass tintColor setter

And for subscript:

extension Matrix {
  subscript (row row: Int) -> [Double] {
    get { ... }
    set { ... }
  }
}
let getRow: (Int) -> () -> [Double] = someMatrix // will pick the
subscript getterlet setRow: (Int) -> ([Double]) -> () = someMatrix //
will pick the subscript setter

Of course is more hard, but there's no new notation, just a expansion of
the current type inference.

Maybe some syntax sugar can be provided in another proposal, but this one
can be the kickoff.

···

Em seg, 28 de dez de 2015 às 16:10, Joe Groff via swift-evolution < swift-evolution@swift.org> escreveu:

On Dec 27, 2015, at 2:47 PM, John McCall <rjmccall@apple.com> wrote:

On Dec 27, 2015, at 10:37 AM, Joe Groff via swift-evolution < > swift-evolution@swift.org> wrote:

   -

   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.

I know this might be too early, but: what syntax are we thinking of for
lenses? We might want to design this with future consistency in mind.

Vaguely, I think it could look something like this. You could define a
lens function by having it return `inout`. Calling the function produces an
lvalue whose access nests within the accesses of its input `inout`
parameters, if any, allowing for things like:

var localVar = 1
let localRef: () -> inout Int = { &localVar }

func second(inout array: [Int]) -> inout Int {
  return &array[1]
}

// Maybe you can define an inout function with accessors too
func fahrenheit(inout celsius: Double) -> inout Double {
  get {
    return celsius * 9/5 + 32
  }
  set {
    celsius = (newValue - 32) * 5/9
  }
}

and you could access the unapplied lens for an instance property using
`Type.property` syntax, analogous to how `Type.method` works. I feel like
if we did that, then it would obviate the need for explicit `property.get`
or `property.set` for most native Swift uses, though maybe not ObjC interop
uses.

-Joe
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[Joe_Groff]

Sent from my iPhone

Sent from my iPhone

We also have a problem with disambiguating same-named members that come from different extensions, whether via protocol extensions or independent concrete extensions from different modules. Could we extend this scheme to allow for disambiguating extension methods by protocol/module name?

That's a fantastic idea!

It does introduce some ambiguities at the margins. Given

  foo.`bar.get`()

Do we look for bar in the lexical scope or in the member scope of foo? Or both with yet another disambiguation mechanism?

I'm still traumatized by implementing the related C++ rules for

  foo.bar::get

:)

Clearly we should just adopt Koenig lookup rules.

This is the other thing that nudges me toward dropping getters/setters from the generalized naming proposal, because it leaves the use of '.' within backticks for your newly-proposed meaning.

Well, even if we drop `.get`/`.set` from the proposal, there's still the potential ambiguity between module names and type or protocol names. As an example from the wild, there's an Either module which defines an Either type, and we have bugs on file saying you can't pick one or the other. It seems like we'll ultimately want some sort of absolute qualification scheme.

-Joe

···

On Dec 29, 2015, at 12:03 PM, Douglas Gregor <dgregor@apple.com> wrote:
On Dec 29, 2015, at 11:03 AM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Dec 29, 2015, at 10:17 AM, Joe Groff <jgroff@apple.com <mailto:jgroff@apple.com>> wrote:

extension ProtocolA { func foo() }
extension ProtocolB { func foo() }

public struct Foo: ProtocolA, ProtocolB {
  func callBothFoos() {
    self.`ProtocolA.foo`()
    self.`ProtocolB.foo`()
  }
}

import A // extends Bar with bar()
import B // also extends Bar with bar()

extension Bar {
  func callBothBars() {
    self.`A.bar`()
    self.`B.bar`()
  }
}

-Joe

On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto: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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  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&gt;
Author(s): Doug Gregor <https://github.com/DougGregor&gt;
Status: Awaiting Review
Review manager: TBD
<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#introduction&gt;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&gt;, continued here <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002203.html&gt;\. See the Alternatives considered <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered&gt; section for commentary on that discussion.

<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#motivation&gt;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&gt;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&gt;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&gt;Alternatives considered

Michael Henson proposed <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html&gt; 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&gt;\. 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&gt; 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

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https://lists.swift.org/mailman/listinfo/swift-evolution

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[Felix_Cloutier1 (Félix Cloutier)]

Currently, they can be disambiguated using (self as ProtocolA).bar(), no?

Félix

···

Le 29 déc. 2015 à 14:10:51, Erica Sadun via swift-evolution <swift-evolution@swift.org> a écrit :

Talk about things you didn't know you needed until you see them. This is a really nice way of disambiguating!

-- E

On Dec 29, 2015, at 12:03 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Sent from my iPhone

On Dec 29, 2015, at 10:17 AM, Joe Groff <jgroff@apple.com <mailto:jgroff@apple.com>> wrote:

We also have a problem with disambiguating same-named members that come from different extensions, whether via protocol extensions or independent concrete extensions from different modules. Could we extend this scheme to allow for disambiguating extension methods by protocol/module name?

That's a fantastic idea!

extension ProtocolA { func foo() }
extension ProtocolB { func foo() }

public struct Foo: ProtocolA, ProtocolB {
  func callBothFoos() {
    self.`ProtocolA.foo`()
    self.`ProtocolB.foo`()
  }
}

import A // extends Bar with bar()
import B // also extends Bar with bar()

extension Bar {
  func callBothBars() {
    self.`A.bar`()
    self.`B.bar`()
  }
}

-Joe

On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto: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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  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&gt;
Author(s): Doug Gregor <https://github.com/DougGregor&gt;
Status: Awaiting Review
Review manager: TBD
<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#introduction&gt;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&gt;, continued here <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002203.html&gt;\. See the Alternatives considered <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered&gt; section for commentary on that discussion.

<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#motivation&gt;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&gt;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&gt;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&gt;Alternatives considered

Michael Henson proposed <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html&gt; 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&gt;\. 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&gt; 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 <mailto:swift-evolution@swift.org>
https://lists.swift.org/mailman/listinfo/swift-evolution

_______________________________________________
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[John_McCall]

Right. I really like this effect.

I’m not that bothered by requiring the backticks, especially because it generalizes well to non-member function references, which I’m not sure any sort of different-member-access syntax does.

John.

···

On Dec 27, 2015, at 4:15 PM, Chris Lattner <clattner@apple.com> wrote:

On Dec 27, 2015, at 4:09 PM, John McCall <rjmccall@apple.com> wrote:

I’m a fan of good error recovery, but I don’t think it is a major concern here for two reasons:

1) The most common case in a method will lack a label, and "thing.foo(_: “ and “thing.foo(:” are both unambiguously a curried reference.
2) A common case of accidentally completing a nullary call (thing.foo() vs thing.foo) will produce a type error. We already produce good QoI for an unapplied function - adding the inverse would be simple.

Further, it will be uncommon *in general* to form a curried reference, so error recovery doesn’t have to be perfect in all the edge cases. As with other commenters, if it is at all possible to avoid the extra backticks, I’d really prefer that.

The concern, I think, is that a messed-up normal call might look like a curried reference.

My inclination would be to go the other way: if we get a syntax for this that we like, I think we should use it for *all* curried member references, and reject things like foo.bar in favor of foo.`bar`. The ability to write foo.bar for a method has always struck me as more clever than wise, to be honest.

If you were to go that far, I’d suggest looking at this as a different version of the “." operator. If you resyntax curried to something else like (just a strawman, intentionally ugly syntax):

  foo.#bar

Then you’d get a nice property that the plain old dot operator always has to be fully applied. This certainly would be a win for error recovery. Also, if you did this, you wouldn’t need the backticks from doug’s proposal either for things like:

  foo.#bar(param1:param2:)

either.

[trs (Thorsten Seitz)]

Much prettier than backticks IMHO.

-Thorsten

···

Am 28.12.2015 um 01:15 schrieb Chris Lattner via swift-evolution <swift-evolution@swift.org>:

(just a strawman, intentionally ugly syntax):

   foo.#bar

[migi (Alex Migicovsky)]

Ah right, great point :-)

- Alex

···

On Dec 28, 2015, at 10:24 AM, Stephen Celis <stephen.celis@gmail.com> wrote:

On Dec 28, 2015, at 11:47 AM, Alex Migicovsky via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Dec 27, 2015, at 1:32 PM, Joe Groff via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> 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.

While the conventions encourage the first parameter to be unlabeled, it doesn't enforce it (and there are exceptions in the standard library, like `removeAll(keepCapacity:)`, as well as `stride(to:…)` and `stride(through:…)`.

Stephen

[Douglas_Gregor]

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.

While the conventions encourage the first parameter to be unlabeled, it doesn't enforce it (and there are exceptions in the standard library, like `removeAll(keepCapacity:)`, as well as `stride(to:…)` and `stride(through:…)`.

Stephen

Ah right, great point :-)

... And initializers, which often have a labeled first argument, also need to fit the syntax.

···

Sent from my iPhone

On Dec 28, 2015, at 9:26 AM, Alex Migicovsky via swift-evolution <swift-evolution@swift.org> wrote:

On Dec 28, 2015, at 10:24 AM, Stephen Celis <stephen.celis@gmail.com> wrote:

On Dec 28, 2015, at 11:47 AM, Alex Migicovsky via swift-evolution <swift-evolution@swift.org> wrote:
On Dec 27, 2015, at 1:32 PM, Joe Groff via swift-evolution <swift-evolution@swift.org> wrote:

- Alex

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[Joe_Groff]

Agreed. I think there are a couple ways to approach that. We could resolve unbound property references contextually, so that Type.property gives you the getter in normal function context, or the lens in inout function context, and/or either allow implicit upconversion from lens to getter function or provide an explicit getter((inout T) -> inout U) -> T -> U adapter function.

-Joe

···

On Dec 28, 2015, at 1:09 PM, Brent Royal-Gordon <brent@architechies.com> wrote:

and you could access the unapplied lens for an instance property using `Type.property` syntax, analogous to how `Type.method` works. I feel like if we did that, then it would obviate the need for explicit `property.get` or `property.set` for most native Swift uses, though maybe not ObjC interop uses.

I feel like if you don't have a way to fetch an unbound getter, you're missing the 90% case, which is constructs like:

  let textValues = textViews.map(.#text.get)

[Douglas_Gregor]

Currently, they can be disambiguated using (self as ProtocolA).bar(), no?

Not if ProtocolA has self requirements or associated types.

···

Sent from my iPhone

On Dec 29, 2015, at 11:48 AM, Félix Cloutier <felixcca@yahoo.ca> wrote:

Félix

Le 29 déc. 2015 à 14:10:51, Erica Sadun via swift-evolution <swift-evolution@swift.org> a écrit :

Talk about things you didn't know you needed until you see them. This is a really nice way of disambiguating!

-- E

On Dec 29, 2015, at 12:03 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org> wrote:

Sent from my iPhone

On Dec 29, 2015, at 10:17 AM, Joe Groff <jgroff@apple.com> wrote:

We also have a problem with disambiguating same-named members that come from different extensions, whether via protocol extensions or independent concrete extensions from different modules. Could we extend this scheme to allow for disambiguating extension methods by protocol/module name?

That's a fantastic idea!

extension ProtocolA { func foo() }
extension ProtocolB { func foo() }

public struct Foo: ProtocolA, ProtocolB {
  func callBothFoos() {
    self.`ProtocolA.foo`()
    self.`ProtocolB.foo`()
  }
}

import A // extends Bar with bar()
import B // also extends Bar with bar()

extension Bar {
  func callBothBars() {
    self.`A.bar`()
    self.`B.bar`()
  }
}

-Joe

On Dec 26, 2015, at 11:22 PM, 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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md

Comments appreciated!

Generalized Naming for Any Function

Proposal: SE-NNNN
Author(s): Doug Gregor
Status: Awaiting Review
Review manager: TBD
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, continued here. See the Alternatives considered section for commentary on that discussion.

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.

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:
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.

Alternatives considered

Michael Henson proposed 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. 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 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

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[Brent_Royal-Gordon]

Currently, they can be disambiguated using (self as ProtocolA).bar(), no?

I think this method is more about, for instance:

  extension NSString {
    func drawAtPoint(point: CGPoint, withAttributes attributes: [String: AnyObject]?) {
      doSomeOtherThing()
      myString.`UIKit.drawAtPoint`(point, withAttributes: attrs)
    }
  }

You use it to access a method by the module it comes from, not the protocol it comes from.

···

--
Brent Royal-Gordon
Architechies

[Felix_Cloutier1 (Félix Cloutier)]

Right.

Félix

···

Le 29 déc. 2015 à 15:04:11, Douglas Gregor <dgregor@apple.com> a écrit :

Sent from my iPhone

On Dec 29, 2015, at 11:48 AM, Félix Cloutier <felixcca@yahoo.ca <mailto:felixcca@yahoo.ca>> wrote:

Currently, they can be disambiguated using (self as ProtocolA).bar(), no?

Not if ProtocolA has self requirements or associated types.

Félix

Le 29 déc. 2015 à 14:10:51, Erica Sadun via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> a écrit :

Talk about things you didn't know you needed until you see them. This is a really nice way of disambiguating!

-- E

On Dec 29, 2015, at 12:03 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Sent from my iPhone

On Dec 29, 2015, at 10:17 AM, Joe Groff <jgroff@apple.com <mailto:jgroff@apple.com>> wrote:

We also have a problem with disambiguating same-named members that come from different extensions, whether via protocol extensions or independent concrete extensions from different modules. Could we extend this scheme to allow for disambiguating extension methods by protocol/module name?

That's a fantastic idea!

extension ProtocolA { func foo() }
extension ProtocolB { func foo() }

public struct Foo: ProtocolA, ProtocolB {
  func callBothFoos() {
    self.`ProtocolA.foo`()
    self.`ProtocolB.foo`()
  }
}

import A // extends Bar with bar()
import B // also extends Bar with bar()

extension Bar {
  func callBothBars() {
    self.`A.bar`()
    self.`B.bar`()
  }
}

-Joe

On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution <swift-evolution@swift.org <mailto: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:

  [swift-evolution] Proposal: Expose getter/setters in the same way as regular methods

the proposal follows, and is available here as well:

  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&gt;
Author(s): Doug Gregor <https://github.com/DougGregor&gt;
Status: Awaiting Review
Review manager: TBD
<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#introduction&gt;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&gt;, continued here <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002203.html&gt;\. See the Alternatives considered <https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#alternatives-considered&gt; section for commentary on that discussion.

<https://github.com/DougGregor/swift-evolution/blob/generalized-naming/proposals/0000-generalized-naming.md#motivation&gt;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&gt;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&gt;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&gt;Alternatives considered

Michael Henson proposed <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html&gt; 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&gt;\. 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&gt; 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

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