[Newbies] 'locking' an object

[Sean Allen]

You'd have to specially code each accessor in that case to check the  
flag.

Ideally I'd like to be able to step in front of every message send to  
descendent objects and
decide whether to pass along ( read call ) or reject ( write call ).

then, all the logic is in one place and the accessors don't need to  
know about what is going on.

any way to do that?

i'm ok with the primitive problem as i don't need real immutability.  
just 'application level' immutability...
ideally, without special coding in every accessor method ( that would  
get tedious very quickly ).


On Oct 2, 2008, at 12:47 PM, Marcin Tustin wrote:

> Surely if you have a wrapper class which only holds a reference to a  
> single object that has all of the data, and that has accessors, then  
> the wrapper can only use the accessors? The data object could have a  
> flag that causes all of the accessors to throw an exception when it  
> is set.
>
> Or am I missing something?
>
> On 10/2/08, Randal L. Schwartz <merlyn at stonehenge.com> wrote:
> >>>>> "Sean" == Sean Allen <sean at monkeysnatchbanana.com> writes:
>
> Sean> If you wanted to take a mutable object and make it immutable  
> and be able
> Sean> to go back again to mutable, how could you do that?
>
> Squeak doesn't have that sort of capability.  The immutability of a  
> few
> classes is because the VM recognizes them specially, and not available
> at the programmer level without modifying the VM.
>
> Other Smalltalk VMs are different.  I think both VisualWorks and  
> GemStone/S
> have primitive bits on an object to be informed when a mutation  
> might be
> attempted.
>
> You can simulate that *mostly* in Squeak by using a "proxy" object  
> that
> intercepts all messages and looks for the dangerous ones, but that's  
> gonna be
> a bit hard to do, and won't be aware of any new code that might call  
> the
> mutating primitives directly.  (*Any* method can call a primitive.)
>
> --
> Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503  
> 777 0095
> <merlyn at stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
> Smalltalk/Perl/Unix consulting, Technical writing, Comedy, etc. etc.
> See http://methodsandmessages.vox.com/ for Smalltalk and Seaside  
> discussion
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