How can I make an existing object read-only?

[Irmen de Jong]

Duncan Booth wrote:
> An alternative is just to pass a copy of the object. That way the recipient 
> can do what they like with it, but the calling code won't see any changes.

Agreed, but then any attempts to change the attributes will go
unnoticed. I wanted a solution that would catch these attempts
and trow an exception (perhaps this wasn't clear enough in
my original question).

Thanks anyway.

--Irmen