>> On Dec 27, 2015, at 10:37 AM, Joe Groff <[email protected]> wrote:
>>
>>
>> On Dec 26, 2015, at 11:22 PM, Douglas Gregor via swift-evolution
>> <[email protected]> wrote:
>>
>> Hi all,
>>
>> Here’s a proposal draft to allow one to name any function in Swift. In
>> effect, it’s continuing the discussion of retrieving getters and setters as
>> functions started by Michael Henson here:
>>
>>
>> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/002168.html
>>
>> 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
>>
[snip]
>
>> 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.
Yes, that seems reasonable.
> 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’m not strongly motivated by it in and of itself; rather, I like the idea of
being able to get at all of the functions (for completeness/consistency),
partly because of the Objective-C selector issue.
> 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,
I should weigh in over on a typed-selectors thread, but my personal view is
that typed selectors are a well-designed feature that isn't worth doing: one
would probably not use them outside of interoperability with Objective-C. To
make that work, we'd need a Clang feature as well (to express the types), then
all of the relevant Objective-C APIs would need to adopt it for us to see the
benefits. On iOS, we are talking about a relatively small number of APIs
(100-ish), and many of those have blocks/closure-based variants that are
preferred.
> and provide API on Selector to grab the individual selectors from that, maybe
> Selector(getterFor: UIView.currentTitle)/(setterFor: UIView.currentTitle)
Sure. I suspect that retrieving the selector of a getter/setter will be fairly
rare, so I'm fine with that operation being ugly.
> . 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.
That is an excellent point. I think you've convinced me to drop the
getter/setter part of this: lenses are the right abstraction for working with
properties, and we can handle ObjC getter/setter in some other way.
>> 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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