[Newbies] 'locking' an object

[Bert Freudenberg]

Am 02.10.2008 um 10:17 schrieb 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?

The proxy Randal was suggesting can do that. It encapsulates an  
object, and decides wether to pass on messages or not.

> 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
>> ______________________________________________