> On Jun 22, 2016, at 9:12 AM, Charlie Monroe <char...@charliemonroe.net> wrote:
>
> Please consider the following code:
>
> let myString: String? = "Hello"
> let anyValue: Any = myString
> let obj: AnyObject? = anyValue as? AnyObject // nil, since it's
> Optional<String>, String being struct,
> // no implicit bridge to AnyObject.
> (myString as AnyObject will
> // create _NSContiguousString).
>
> if let optionalAny: AnyObject? = anyValue as? AnyObject? { // Error - can't
> downcast from Any
> // ...
> }
>
> if let optionalAny: AnyObject? = anyValue as? AnyObject { // nil
> // ...
> }
>
> if let optionalAny: AnyObject? = asOpt(anyValue) { // Optional<AnyObject>
> if let value = optionalAny { // value is _NSContiguousString
> value.dynamicType
> }
> }
>
> This behavior is IMHO incosistent at best. Should this be considered correct
> behavior or a compiler bug?
The inability to cast from Any to an optional is a bug.
John.
>
>> On Jun 22, 2016, at 5:59 PM, L. Mihalkovic <laurent.mihalko...@gmail.com
>> <mailto:laurent.mihalko...@gmail.com>> wrote:
>>
>>
>>
>> On Jun 22, 2016, at 5:51 PM, John McCall <rjmcc...@apple.com
>> <mailto:rjmcc...@apple.com>> wrote:
>>
>>>
>>>> On Jun 22, 2016, at 12:15 AM, L. Mihalkovic via swift-evolution
>>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
>>>>
>>>> Func asOpt<T>(v:Any) -> Optional<T> {
>>>> If let val = v as? T {
>>>> Return val
>>>> }
>>>> Return nil
>>>> }
>>>> Regards
>>>> LM
>>>> (From mobile)
>>>
>>> This is just:
>>> return v as? T
>>
>> Had more code where i took it from... I thk it is one of these simple thgs
>> that u never forget but may not be immediate to thk abt. Maybe worth adding
>> to doc comment for Optional<> (forgive if is there already)
>>
>>>
>>> John.
>>>
>>>>
>>>> On Jun 22, 2016, at 7:11 AM, Charlie Monroe via swift-evolution
>>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
>>>>
>>>>> Unfortunately, this is not as easy, because automatic bridging won't be
>>>>> applied:
>>>>>
>>>>> let myString: String? = "Hello"
>>>>> let anyValue: Any = myString
>>>>>
>>>>> myString as? AnyObject // _NSContiguousString
>>>>> anyValue as? AnyObject // nil, since String is struct
>>>>>
>>>>> let array: [String]? = ["Hello"]
>>>>> let anyArray: Any = array
>>>>> anyArray as? AnyObject // nil
>>>>> anyArray as? [AnyObject] // nil
>>>>> array as? AnyObject // ["Hello"]
>>>>>
>>>>> And this goes for strings, arrays, dictionaries and possibly other types.
>>>>> Which means that you need to handle manually all of the bridging to ObjC
>>>>> types, which has really grown in Swift 3, taking into account all the
>>>>> Foundation types that are now structs.
>>>>>
>>>>> Should this then be considered compiler bug that bridging isn't taken
>>>>> into account?
>>>>>
>>>>> Nevertheless, I'd still find it useful exposing the isOptional() function
>>>>> as well as the asOptional which would allow a cast from Any to
>>>>> Optional<Any> which is not possible at all at this moment since any such
>>>>> cast will pick up the Optional first:
>>>>>
>>>>> let myString: String? = "Hello"
>>>>> let anyValue: Any = myString
>>>>> if let value = anyValue as? Any {
>>>>> value.dynamicType // This is still Optional<String>, not naively just
>>>>> the value of the optional
>>>>> }
>>>>>
>>>>>
>>>>>
>>>>>> On Jun 21, 2016, at 8:18 PM, Joe Groff <jgr...@apple.com
>>>>>> <mailto:jgr...@apple.com>> wrote:
>>>>>>
>>>>>> 'as?' should already do this. If you have an Any that contains an
>>>>>> Optional<T> and cast 'any as? T', you'll get the value inside the
>>>>>> Optional if there is one, or the cast will fail if the optional is nil
>>>>>> or the type doesn't match.
>>>>>>
>>>>>> -Joe
>>>>>>
>>>>>>> On Jun 20, 2016, at 11:00 PM, Charlie Monroe via swift-evolution
>>>>>>> <swift-evolution@swift.org <mailto:evolut...@swift.org>> wrote:
>>>>>>>
>>>>>>> I've recently written a CoreData editor on iOS which automatically
>>>>>>> generates UI based on the model which is described using classes such
>>>>>>> as PrimitiveProperty, etc. Since it automatically sets the value on the
>>>>>>> entity, it needs to convert the value to AnyObject in order to pass it
>>>>>>> to setValue(_:forKey:), so it needs to be able to detect whether the
>>>>>>> value is Optional and in case it is, either transform the non-nil value
>>>>>>> to AnyObject (String -> NSString, Array -> NSArray, ...). Which is
>>>>>>> currently really hard to achieve:
>>>>>>>
>>>>>>> var obj: IndexPath? = IndexPath()
>>>>>>> let anyValue: Any = obj
>>>>>>> anyValue.dynamicType /// Optional<Foundation.IndexPath>.Type
>>>>>>>
>>>>>>> /// Using only anyValue, determine if it's Optional and retrieve its
>>>>>>> value if
>>>>>>> /// non-nil as AnyObject.
>>>>>>> func isOptional(anyValue: Any) -> Bool {
>>>>>>> // Error: Cannot downcast from 'Any' (aka 'protocol<>') to a more
>>>>>>> // optional type 'Optional<_>'
>>>>>>> return anyValue is Optional
>>>>>>> return anyValue as? Optional != nil
>>>>>>> ...
>>>>>>> }
>>>>>>>
>>>>>>> Unless there are major reasons why it's not exposed, I'd propose
>>>>>>> introducing a new function isOptional(anyValue: Any) -> Bool, which
>>>>>>> would simply call Builtin.isOptional just like _isOptional does in
>>>>>>> Builtin.swift. (which pretty much is just taking the current
>>>>>>> _isOptional, removing underscore and marking it public).
>>>>>>>
>>>>>>> However, this still doesn't help with the issue of retrieving the value
>>>>>>> of the Optional. You now know the value in `anyValue` is Optional, but
>>>>>>> there is no good way to cast it to e.g. Optional<AnyObject>. Here we're
>>>>>>> getting into a vicious cycle that Any can be an Optional which is Any.
>>>>>>>
>>>>>>> My second part of the proposal introduces another function:
>>>>>>>
>>>>>>> func asOptional<T>(anyValue: Any) -> Optional<T>?
>>>>>>>
>>>>>>> Which will:
>>>>>>> - return nil if !isOptional(anyValue)
>>>>>>> - return a non-nil value only if `anyValue` contains in fact an
>>>>>>> Optional of type T.
>>>>>>>
>>>>>>> Usage:
>>>>>>>
>>>>>>> if let anyObjOptional: AnyObject? = asOptional(anyValue: anyValue) {
>>>>>>> if let anyObj = anyObjOptional {
>>>>>>> // anyObj is now the actual content of the optional.
>>>>>>> }
>>>>>>> }
>>>>>>>
>>>>>>> As a sidenote, this is my current workaround:
>>>>>>>
>>>>>>> private protocol _XUOptional {
>>>>>>> var objectValue: AnyObject? { get }
>>>>>>> }
>>>>>>>
>>>>>>> extension Optional: _XUOptional {
>>>>>>> var objectValue: AnyObject? {
>>>>>>> switch self {
>>>>>>> case .None:
>>>>>>> return nil
>>>>>>> case .Some(_):
>>>>>>> return self! as? AnyObject
>>>>>>> }
>>>>>>> }
>>>>>>> }
>>>>>>>
>>>>>>> if let optional = anyValue as? _XUOptional {
>>>>>>> let object = optional.objectValue
>>>>>>> /// ...
>>>>>>> }
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> swift-evolution mailing list
>>>>>>> swift-evolution@swift.org <mailto:swift-evolution@swift.org>
>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>> <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>>>>>
>>>>>
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>
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