As I see it, this is serious bug. In Swift 3.0, parameter labels (or lack of 
them) are supposed to be a part of the function name. 
Otherwise, the two `key` definitions would create a name collision and should 
have been rejected in the first place. This should not happen, because only 
`key(at:)` should be treated as a method pointer and not `key`. Even the 
following example:

protocol QueryRow {
    var key: Any { get }
    func key(_ index: UInt) -> Any?
}

should not create a collision as method pointer now is `key(_:)` and not `key`. 
I guess the reason this is happening is some attempt at backward compatibility, 
but this is clearly causing a serious bug. Have you reported it?

> On Sep 13, 2016, at 1:13 PM, Jens Alfke via swift-users 
> <swift-users@swift.org> wrote:
> 
> One of my co-workers just noticed a problem with the (bridged) API of our 
> Objective-C framework, when used from Swift 3 (but not earlier). We have a 
> class CBLQueryRow that includes the following:
> 
>       @property (readonly) id key;
>       - (nullable id) keyAtIndex: (NSUInteger)index;
> 
> In Swift this becomes
>       open var key: Any { get }
>       open func key(at index: UInt) -> Any?
> 
> The problem is that any reference to `key` now seems to refer to a pointer to 
> the method, not to the property, leading to compiler diagnostics like the 
> following (where `row` is a CBLQueryRow):
> 
> TaskListsViewController.swift:95:40: warning: cast from '(UInt) -> Any?' to 
> unrelated type 'String' always fails
>         cell.textLabel?.text = row.key as? String
>                                ~~~~~~~ ^   ~~~~~~
> That’s a warning not an error, but obviously at runtime the `as?` would 
> always fail and result in nil.
> 
> This is rather bad for us, since the `key` property is a crucial part of the 
> API, while the `key()` method that pre-empts it is obscure and little-used.
> 
> I can reproduce this in a playground in Xcode 8 like so:
> 
> protocol QueryRow {
>     var key: Any { get }
>     func key(at index: UInt) -> Any?
> }
> 
> var row: QueryRow
> 
> row.key as? String
> In addition to the valid error about `row` being uninitialized, I also get 
> the cast failure.
> 
> What’s the best workaround for this?
> 
> —Jens
> _______________________________________________
> swift-users mailing list
> swift-users@swift.org
> https://lists.swift.org/mailman/listinfo/swift-users

_______________________________________________
swift-users mailing list
swift-users@swift.org
https://lists.swift.org/mailman/listinfo/swift-users

Reply via email to