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[Caml-list] copy of parametrized object
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Date: -- (:)
From: Bow-Yaw Wang <bywang@s...>
Subject: [Caml-list] copy of parametrized object

Hi,

I'd like to know how to make independent copies of parameterized 
objects. Consider the following example:

# class ['a] t = object method id (x:'a) = x end;;
class ['a] t : object method id : 'a -> 'a end
# let o = new t;;
val o : '_a t = <obj>
# let p = Oo.copy o;;
val p : < id : '_a -> '_a > = <obj>
# o#id 1;;
- : int = 1

After defining a simple parameterized class t, I create an
object o of type '_a t and make p as a copy. After the type 
'_a is instantiated to int, I'd expect p to retain its type
< id : '_a -> '_a >. However, 

# p;;
- : < id : int -> int > = <obj>

So my questions are:

1. Is there a way to make a copy of o so that it can be 
instantiated differently?
2. If not, is there any type-theoretic explanation? I'm
just curious if it may make type system unsound.

I'm aware of polymorphic methods. Unfortunately, the
project I'm working on uses parameterized classes. Using
polymorphic methods doesn't seem to be feasible at the
moment. :(

Thanks in advance,

Bow-Yaw

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