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Subject: RE: [Caml-list] Deep copy
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Date: Mon, 15 Jul 2002 17:24:57 +0200
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Thread-Topic: [Caml-list] Deep copy
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From: "zze-MARCHEGAY Michael stagiaire FTRD/DTL/LAN" <michael.marchegay@rd.francetelecom.com>
To: "Eray Ozkural" <erayo@cs.bilkent.edu.tr>
Cc: <caml-list@inria.fr>
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> De : Eray Ozkural [mailto:erayo@cs.bilkent.edu.tr]
> Envoy=E9 : lundi 15 juillet 2002 17:03
>=20
>=20
> On Monday 15 July 2002 13:06, zze-MARCHEGAY Michael stagiaire=20
> FTRD/DTL/LAN=20
> wrote:
> > Hi all,
> >
> > I'm writting a program that manipulates a graph structure=20
> and I need to
> > make deep copies of some of the graph nodes. The function=20
> Oo.copy donesn't
> > perform a deep copy and I haven't found any other that=20
> could make it.
>=20
> You mean something like creating a new object on the heap and=20
> copying over the=20
> contents of an existing object.
>=20
> If this were C++ all you had to do would be invoking the copy=20
> constructor
>  Node* x =3D new Node(old_node);
>=20
> From the documentation OO.copy does look like a deep copy operation:
>=20
> val copy : < .. > -> < .. >
> Oo.copy o returns a copy of object o, that is a fresh object=20
> with the same=20
> methods and instance variables as o

In fact, if an object 'a' contains an attribute 'b' that is another=20
object, Oo.copy on 'a' gives a copy of 'a' in which the attribute
'b' is **physically** equal to the copied attribute from 'a'.

Example:
class a =3D=20
  object=20
    val mutable b =3D new b
    method get_b =3D b
  end
and b =3D=20
  object
    val mutable c =3D "1"
    method set_c x =3D  c <- x
    method print_c =3D print_string ("c=3D" ^ c ^ "\n") =20
  end

let aa =3D new a
let aa' =3D Oo.copy aa

let _ =3D=20
  aa#get_b#set_c "3";
  aa#get_b#print_c;
  aa'#get_b#print_c

gives:
c=3D3
c=3D3

whereas a deep copy would give:
c=3D3
c=3D1

>=20
> Curious,
> =20
> --=20
> Eray Ozkural <erayo@cs.bilkent.edu.tr>
> Comp. Sci. Dept., Bilkent University, Ankara
> www: http://www.cs.bilkent.edu.tr/~erayo
> GPG public key fingerprint: 360C 852F 88B0 A745 F31B  EA0F=20
> 7C07 AE16 874D 539C
>=20
>=20
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