[Newbies] 'locking' an object

[Marcin Tustin]

On Thu, Oct 2, 2008 at 6:17 PM, Sean Allen <sean at monkeysnatchbanana.com>wrote:

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

Yes. This is unlikely to be a problem unless you have a lot of members.

Alternatively you could adapt the code that generates your accessors to put
in that check, or you could use/adapt magritte to generate your objects.


>
> 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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>
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