Ext Optional {
Func ifUnwraps<T>(_ h: T->()){
Switch self
Case .Some(let v):
If let t=v as? T { h(t) } // invoke if T matches
Def:
Brk
}
Regards
LM
(From mobile)
> On Jun 22, 2016, at 9:15 AM, L. Mihalkovic <[email protected]>
> wrote:
>
> 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
>>
>> _______________________________________________
>> swift-evolution mailing list
>> [email protected]
>> https://lists.swift.org/mailman/listinfo/swift-evolution
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