[swift-users] Foundation bug or indended?

[Jordan Rose]

It's semi-intended. When the compiler imports (NS)Operation into Swift, it uses the Swift naming convention…but it also declares a property with the old name, 'executing', in order to give better error messages if someone tries to use the Objective-C name. That's what's colliding with your private 'executing' property.

We should improve this experience on the compiler side, either by having a 'nonoverride' attribute or similar, or just by noting that you wouldn't try to override something with a private property not declared 'override' in the first place. But since the workaround is so simple it hasn't been a priority.

Sorry for the trouble,
Jordan


> On Sep 4, 2017, at 05:01, Adrian Zubarev via swift-users <swift-users at swift.org> wrote:
> 
> Hi there,
> 
> before filing a new issue I would like to ask if this is intended behaviour or a bug:
> 
> The Foundation class Operation which has it’s roots in Objective-C has a few readonly properties like the following one:
> 
> @available(iOS 2.0, *)
> open class Operation : NSObject {
>     ...
>     open var isExecuting: Bool { get }
>     ...
> }
> On the other hand the Objective-C header looks like this:
> 
> NS_CLASS_AVAILABLE(10_5, 2_0)
> @interface NSOperation : NSObject {
> ...
> @property (readonly, getter=isExecuting) BOOL executing;
> ...
> @end
> Now I want to create a custom subclass of Operation and override isExecuting, everything works fine until I try to create a private stored property named executing:
> 
> final class TransitionOperation : Operation {
>     // error: cannot override with a stored property 'executing'
>     private var executing = false
> 
>     override var isExecuting: Bool {
>         ...
>     }
> }
> I’m a little bit confused here:
> 
> Is this intended behaviour or a bug?
> The Foundation implemented in Swift is not used for iOS deployment, instead the Obj-C one is used right?
> 
> 
> 
> 
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