Re: [Pharo-users] Is it possible to follow an object through a computation?

[Marcus Denker via Pharo-users]

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> On 3 Jan 2019, at 03:17, Esteban Maringolo <emaring...@gmail.com> wrote:
> 
> Hi Paul,
> 
> You can set the object to be "read only" (aka "immutable") and handle the 
> exception.
> 
> E.g.
> 
> | u |
> u := User named: 'Paul'.
> u beReadOnlyObject.
> [ "your code modifying u's state" ]
>       on: ModificationForbidden 
>       do: [ :ex | 
>               ex halt.
>                "inspect state" 
>               u beWritableObject.
>               ex resume
>        ].
> 
> Probably there is a better way to do this with slots, using default ones or 
> subclassing `InstanceVariableSlot` for that instance only and halting on the 
> `write:to:` method of it.
> 

I started an experiment to turn the read Only mechanism into a general object 
change notifier:

https://github.com/MarcusDenker/ChangeDetector

This allows the following style of use:


testObserveObjectWithModification [
        | observed observer |
        observed := 'test2'.
        observer := self.
        observed notifyOnChange: observer.
        "the observed object is now read only"
        self assert: (observed isReadOnlyObject).
        "but we can change it!"
        observed at: 1 put: $T.

        self assert: observed equals: 'Test2'.
        "and the method #objectChangeNotified was called, setting flag"
        self assert: flag equals: #yes.
        
        observed stopNotifyOnChange: observer.
        self deny: (observed isReadOnlyObject).


missing:

-> we need to model read only for all tracked object (we need to remember the 
old state and restore it)
-> think about threads… is there a problem?


        Marcus

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