[swift-users] didSet and time when propagation of mutation happens

[Zhao Xin]

I think the order is right.

value.set >> value.didSet >> string.set >> string.didSet

you expected value.set >> string.set >>  value.didSet >> string.didSet is
not correct.

The value "1" is not you expected. However, that is something that I think
is tricky. For closure

>  {
>     print(myClass.myString.value)
> }

it captured the value. However, unless Objective-C, Swift will decide if it
is a static capture or an inout capture. So it should be consider right to
 be "1" or "2"? I am not sure about that.

Zhaoxin

On Thu, Jul 14, 2016 at 8:36 AM, Diego Sánchez <swift-users at swift.org>
wrote:

> Hi all,
>
> The following snippet summarises an issue I was investigating:
>
> struct Observable<T> {
>     var value: T {
>         didSet {
>             print("Observable.didSet")
>             callback?()
>         }
>     }
>     var callback: (() -> Void)?
> }
>
> class MyClass {
>     var myString: Observable<String> {
>         get {
>             return _myString
>         }
>         set {
>             print("MyClass.Setter")
>             self._myString = newValue
>         }
>     }
>
>     private var _myString: Observable<String>
>     init (string: Observable<String>) {
>         self._myString = string
>         print("MyClass.init.end")
>     }
> }
>
> let myClass = MyClass(string: Observable<String>(value: "1", callback:
> nil))
> myClass.myString.callback = {
>     print(myClass.myString.value)
> }
> myClass.myString.value = "2"
>
> *Output:*
> MyClass.init.end
> MyClass.Setter
> Observable.didSet
> *1*
> MyClass.Setter
>
> Obviously I wasn't expecting to get "1", but "2" in the callback's print,
> and this happens because MyClass.setter is called after Observable.didSet
> completes.
>
> Is it feasible that all the *set*s are called first, and then all the
> *didSet*s?
>
> Cheers,
> Diego
>
> _______________________________________________
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> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
>
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