> On Dec 26, 2015, at 11:48 PM, Douglas Gregor via swift-evolution > <swift-evolution@swift.org> wrote: > > Hi all, > > Currently, producing an Objective-C selector in Swift is an error-prone > operation. One effectively just writes a string literal and uses it in a > context where an ObjectiveC.Selector is expected: > > control.sendAction(“doSomething:”, to: target, forEvent: event) > > There are many points of failure here: > > 1) The compiler doesn’t syntax-check at all to make sure it’s a valid > spelling for a selector > 2) The compiler doesn’t look for existing methods with this selector anywhere > 3) The mapping from a Swift method name to an Objective-C selector isn’t > always immediately obvious (especially for initializers), and will be getting > significantly more complicated with the renaming work for Swift 3 > (https://github.com/apple/swift-evolution/blob/master/proposals/0005-objective-c-name-translation.md). > > I suggest that we add an expression ‘objc_selector(method-reference)` that > produces the Objective-C selector for the named method, and produces an error > if the method does not have an Objective-C entry point. For example: > > control.sendAction(objc_selector(MyApplication.doSomething), to: > target, forEvent: event) > > “doSomething” is a method of MyApplication, which might even have a > completely-unrelated name in Objective-C: > > extension MyApplication { > @objc(jumpUpAndDown:) > func doSomething(sender: AnyObject?) { … } > } > > By naming the Swift method and having objc_selector do the work to form the > Objective-C selector, we free the programming from having to do the naming > translation manually and get static checking that the method exists and is > exposed to Objective-C. > > This proposal composes with my “Generalized Naming for Any Function” > proposal, which lets us name methods fully, including getters/setters: > > let sel1: Selector = objc_selector(UIView.`insertSubview(_:at:)`) // > produces the Selector “insertSubview:atIndex:" > let sel2: Selector = objc_selector(UIView.`frame.get`) // produces the > Selector “frame" > > I don’t like the `objc_selector` syntax at all, but otherwise I think this > functionality is straightforward.
Selectors can be seen as "just" a kind of function value. Do we need a new syntax form at all? We ought to be able to turn an unbound function reference like UIView.insertSubview into a selector reference in Selector type context, or maybe a typed @convention(selector) function as discussed in another thread, without any explicit get-a-selector operation. -Joe _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
