Zhao_Xin
(Zhao Xin)
1
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?
Zhaoxin
jrose
(Jordan Rose)
2
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
···
On May 25, 2016, at 02:11, zh ao via swift-users <swift-users@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?
