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@stonehenge.com wrote:
"Sean" == Sean Allen sean@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.)
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