C++Talk.NET

Radu Grigore · Guest

Is it possible to write a class LazyCopy that can be used like in the
following code? Or at least something similar?

--------
class Obj
{
public:
Obj() {val = 0;}
Obj(const Obj& other) {val = other.val; }
void SetValue(int val_) {val = val_; }
int GetValue() const;
private:
int val;
}

LazyCopy<Obj> a(new Obj());
LazyCopy<Obj> b, c, d;
a.SetValue(10);
[1] b = c = d = a;
cout << c.GetValue() << endl; // writes 10
cout << a.GetValue() << endl; // writes 10

[2] c.SetValue(20);
cout << c.GetValue() << endl; // writes 20
cout << a.GetValue() << endl; // writes 10
-----------
At line [1] there is only one object Obj and all four identifiers a,
b, c, d refer to it. At line [2] there are two objects: one refered by
a, b, and d; the other refered by c.

In order to achive this you need to distinguish between a const method
(eg. GetValue) and a non-const method (eg. SetValue) somewhere in
LazyCopy. This is needed because a copy should be created whenever an
object from a collection (collection = one object, ref counted) is
mutated.

regards,
radu
http://www.geocities.com/_rgrig

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]