Hi Marcel,

That's a bug. The argument of #becomeForward: is never attempted to be 
modified. The following should work:

| a |
a := Object new.
a becomeForward: #foo.
self assert: a = 'foo'.

The error it raises is nonsense.


Levente

On Tue, 14 Apr 2020, Marcel Taeumel wrote:

> Hi, all!
> 
> I suppose that since ModificationForbidden and read-only objects, the following is no longer possible:
> 
> MyExternalResource allInstancesDo: [:resource |
>    resource becomeForward: #notAvailable].
> 
> What to do now? Introduce a custom, mutable, placeholder object instead?
> 
> Best,
> Marcel
> 
>