/*
I'm sure this question has come up before, but I can't find it back in my
archive. It has to do with making smart pointers behave like normal pointers.
In particular, you can assign a normal pointer to a derived class object to
a pointer to a base class object. This is not possible when
a so-called smart pointer class (a class embedding a pointer
to the actual object with some extra behaviour if required) is used.
In the program below, I've used a template class for the smart pointer class
and this makes it even worse.

Overloading a cast operator at file scope could help me, but this
is not possible.

Also, an explicit cast like "baseptr1 = (Ptr<Base>) derivedptr1;" is
disallowed.

Can someone tell me how to resolve the problem? Is the standard
adapted in any way to resolve the problem?

Thanks in advance,

Johan

*/

#include <iostream.h>

class Base { };
class Derived : public Base { };

template <class Type>  // smart pointer class definition
class Ptr
{
  public:
 Ptr(Type* ptr1) : ptr(ptr1) { }
  private:
 Type* ptr;
};

/*
operator Ptr<Base> (Ptr<Derived> derivedptr)
{
 return (Ptr<Base>) derivedptr;
}
 // overloading a cast operator at file scope is not possible
*/

main()
{
 Base abase;
 Derived aderived;

// with ordinary pointers:

 Base*   abasep1 = &abase;
 Derived*  aderivedp1 = &aderived;

 abasep1 = (Base*) aderivedp1; // explicit casting is superfluous
 abasep1 = aderivedp1;

// with smart pointers:

 Ptr<Base> abaseptr1 = &abase;
 Ptr<Derived> aderivedptr1 = &aderived;

// abaseptr1 = (Ptr<Base>) aderivedptr1; // not allowed
// abaseptr1 = aderivedptr1; // not possible because I'm
     // unable to provide a cast operator
 return 0;
}



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Johan Vanslembrouck - SE99            Tel    : +32 3 2407739
Alcatel Bell Telephone                Telex  : 72128 Bella B
Francis Wellesplein  1                Fax    : +32 3 2409932
B-2018 Antwerp                        e-mail : jvsb@sebb.bel.alcatel.be
Belgium
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