Func asOpt<T>(v:Any) -> Optional<T> {
If let val = v as? T {
Return val
}
Return nil
}
Regards
LM
(From mobile)
> On Jun 22, 2016, at 7:11 AM, Charlie Monroe via swift-evolution
> <[email protected]> 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 <[email protected]> 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
>>> <[email protected]> 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
>>> [email protected]
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>
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