[swift-evolution] Remove AnyObject Constraint for Objective-C Lightweight Generics

[Charles Srstka]

> On Nov 8, 2017, at 10:51 PM, Charlie Monroe via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I find more limiting the ability not to declare @objc a property of a class that doesn't inherit from NSObject:
> 
> class Foo {
> 	var x: Int = 0
> }
> 
> class Bar {
> 	var foo = Foo() // Why shouldn't we allow this @objc? 
> }
> 
> or
> 
> protocol BarProtocol: AnyObject {
> 	func fooDidBar(_ foo: Foo)
> }
> 
> class BarContoller: NSViewController {
> 	@IBOutlet weak var delegate: BarProtocol? // Error - not expressible in ObjC.
> }
> 
> While Foo doesn't inherit from NSObject, it still can have @objc members used for binding. I have quite few classes that need to inherit from NSObject just for that purpose.
> 
> I fully understand the logic behind it that it needs to be exported to ObjC headers and runtime metadata, but I'd prefer these being exported as (id) into ObjC rather than not allowing this at all as these are all objects that can be passed into the ObjC world...

+1000. In addition to the issues raised above, this limitation wreaks havoc with my attempts to properly support KVO in Swift projects. You either have to create a second Any-typed property, bloating the interface, or you have to go with the old string-based key path API, which also locks you out of using the Swift 4 closure-based observers.

Charles

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