There is probably no sensible answer to the question in my former mail:

In the case of parameterized classes it would be impossible to call a
constructor of type 'self (unknown number/type of parameters). Could
have thought about this faster... ;-)

Hm, I fear the only way to get the intended result without too much
effort is to restrict the interface of the self-object when it is passed
to another instance of its class...

Best regards,
Markus Mottl

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl