[swift-users] Bool with Foundation framework, can convert to AnyObject

[zh ao]

Thanks, Jordan.

Zhaoxin

On Thu, May 26, 2016 at 12:33 AM, Jordan Rose <jordan_rose at apple.com> wrote:

>
> On May 25, 2016, at 02:11, zh ao via swift-users <swift-users at swift.org>
> wrote:
>
> We were told that Bool can't downcast to AnyObject in Swift. However, with
> Foundation framework, we can.
>
> do {
>     let a:Bool = true
>     let object:AnyObject = a as AnyObject
>     object.dynamicType
>     // __NSCFBoolean.Type
>     let b:Bool = object as! Bool
>     b // true
> }
>
> This feature works in some code automatically (like in a Dictionary), but
> in some other codes(like in a function), you have to downcast it yourself.
>
> do {
>     var dictionary = Dictionary<String, AnyObject>()
>
>
>     func update<T:AnyObject>(value:T, key:String) {
>         dictionary.updateValue(value, forKey: key)
>     }
>
>
>     let aBool = true
>     let key = "testBool"
>
>
>     dictionary.updateValue(aBool, forKey: key)
>     // works
>
>
>     update(aBool, key: key)
>     // doesn't work. cannot invoke 'update' with an argument list of type
> '(Bool, key: String)'
>
>
>     update(aBool as AnyObject, key:key)
>     // works
>
> }
>
> My question: Is this normal? Should it all be automatic or not?
>
>
> This is expected behavior: when you explicitly coerce (using ‘as’) or cast
> (using ‘as’ or ‘as!’), Bool can be converted to an NSNumber and from there
> up to AnyObject. Since NSNumber is part of Foundation, you need to have
> Foundation imported to do this.
>
> We’re still deciding whether the conversion from Bool to NSNumber (and
> similar "bridging conversions") should be implicit or explicit. The
> conversion from NSNumber to Bool has been explicit for a while now.
>
> Jordan
>
>
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