Inheritance Issues

[Matthew]

Hi, I have a base class called Item with a virtual function act. It's
subclass Sword defines the function again doing something different
from the first. It store the sword in a vector of items and call the
act function and, as to be expected, it calls the one from Item. How
can I get it to call the one from sword?

[Russ Ford]

Re: Inheritance Issues

On 20 Nov 2003 12:50:00 -0800, mattheww@nessin ess.com (Matthew) wrote:

Did you declare act as virtual in the Sword class?
[color=blue]
>Hi, I have a base class called Item with a virtual function act. It's
>subclass Sword defines the function again doing something different
>from the first. It store the sword in a vector of items and call the
>act function and, as to be expected, it calls the one from Item. How
>can I get it to call the one from sword?[/color]

[Mike Wahler]

Re: Inheritance Issues


"Russ Ford" <russford@shaw. ca> wrote in message
news:igbqrvcmg2 2k6kmoijt5lpdfv mh4c00lbq@4ax.c om...[color=blue]
> On 20 Nov 2003 12:50:00 -0800, mattheww@nessin ess.com (Matthew) wrote:
>
> Did you declare act as virtual in the Sword class?[/color]

Not necessary (as long as the signature is the same).

The real issue is: *How* was the function called?
Polymorphism only works via a pointer or reference.

Matthew:

We can only make guesses like this since you show no code.

Show the code.

-Mike

[Mike Wahler]

Re: Inheritance Issues


"Mike Wahler" <mkwahler@mkwah ler.net> wrote in message
news:qpavb.8552 $n56.1935@newsr ead1.news.pas.e arthlink.net...[color=blue]
>
> "Russ Ford" <russford@shaw. ca> wrote in message
> news:igbqrvcmg2 2k6kmoijt5lpdfv mh4c00lbq@4ax.c om...[color=green]
> > On 20 Nov 2003 12:50:00 -0800, mattheww@nessin ess.com (Matthew) wrote:
> >
> > Did you declare act as virtual in the Sword class?[/color]
>
> Not necessary (as long as the signature is the same).[/color]

Clarification: if the signature is not the same, then
it's not an override anyway.

-Mike

[lilburne]

Re: Inheritance Issues

Matthew wrote:
[color=blue]
> Hi, I have a base class called Item with a virtual function act. It's
> subclass Sword defines the function again doing something different
> from the first. It store the sword in a vector of items and call the
> act function and, as to be expected, it calls the one from Item. How
> can I get it to call the one from sword?[/color]

If you have vector<Item> then you are stuffed because what
is stored in the vector is Item's the Sword part is stripped
off, lookup class slicing (no pun intended) in your book.
What you want is either a vector of pointer to Items
vector<Item*>, or more preferably a vector<
smart_pointer<I tem> >. Where 'smart_pointer' is your
favourite wrapper for pointers (boost::shared_ ptr at a pinch
I suppose).

[jeffc]

Re: Inheritance Issues


"Mike Wahler" <mkwahler@mkwah ler.net> wrote in message
news:vqavb.8555 $n56.6612@newsr ead1.news.pas.e arthlink.net...[color=blue]
>
> "Mike Wahler" <mkwahler@mkwah ler.net> wrote in message
> news:qpavb.8552 $n56.1935@newsr ead1.news.pas.e arthlink.net...[color=green]
> >
> > "Russ Ford" <russford@shaw. ca> wrote in message
> > news:igbqrvcmg2 2k6kmoijt5lpdfv mh4c00lbq@4ax.c om...[color=darkred]
> > > On 20 Nov 2003 12:50:00 -0800, mattheww@nessin ess.com (Matthew) wrote:
> > >
> > > Did you declare act as virtual in the Sword class?[/color]
> >
> > Not necessary (as long as the signature is the same).[/color]
>
> Clarification: if the signature is not the same, then
> it's not an override anyway.[/color]

If it's not virtual, it's never an override regardless of the signature.