override virtual, covariant return type

[David Sobey]

Hi everyone

I'm having huge difficulties overriding a virtual function with a function
that returns a covariant type. I'd be grateful if someone could show me some
code where this is done:
- A class BaseClass is declared with a function me() that takes no arguments
and returns itself, or a pointer or reference to itself.
- A derived class DerivedClass that override me() that takes no arguments
and returns itself, a pointer or reference to itself ("itself" being the
instance of the derived class)
- A piece of code like this: (Warning: this is PSUEDOCODE)
BaseClass foo=new DerivedClass
foo.me() <-this should return a pointer or reference or instance of type
DerivedClass.

I would be VERY VERY gratefull if someone could help me with this
confounding problem, be it in C++ or C#.

Cheers
dave

[David White]

"PV" <pv******@shaw. ca> wrote in message
news:nuY2e.8604 62$Xk.481117@pd 7tw3no...

Try this: (simple and stupid, but it does what you want)

[snip]

I used to do this before there was a dynamic_cast, or when my compiler
didn't have dynamic_cast, but I didn't like it for the reason that Andrew M.
gave. Now I can't see why this would ever be preferred to dynamic_cast.

DW

[David White]

I wrote in message news:Yg******** **********@nasa l.pacific.net.a u...

"David Sobey" <ds****@NOSPAMu grad.unimelb.ed u.au> wrote in message
news:42******** @dnews.tpgi.com .au...

code where this is done:
- A class BaseClass is declared with a function me() that takes no
arguments and returns itself, or a pointer or reference to itself.
class BaseClass
{
public:
virtual BaseClass *me() const { return new BaseClass(*this ); }
// more members
};

[snip]
It is the convention to name such a virtual function 'clone' rather than
'me'.

Sorry, I misunderstood that a clone function was requested, but it really
was a 'me' function. It doesn't affect the rest of my answers though.

DW

[David Sobey]

This would be preffered because when there are lots and lots of direct
children of base class, ie lots of DerivedClass's, and a function that
excepts two BaseClass pointers as it's arguments, dynamic_casting would be a
nightmare, as there would be an exponential number of combinations of
casting.

cheers
dave