yade-dev team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

2010/5/17 Václav Šmilauer <eudoxos@xxxxxxxx>

>
> > Ok. So is the derived class object also a base class object? Exactly
> > the same one?
>
> You can always cast derived object to an instance of its base class,
> that is the interest of inheritance, actually one of the most basic
> principles of object-oriented programming.
>
> Think of casting as changing point of view; a doctor can see his friend
> as his friend, or as a concrete patient, or as an instance of generic
> mankind species, depending on what he needs.
>
> That happens when you cast. static_cast<FrictPhys*>(..) says that now
> you want to see that object as a pointer to FrictPhys (heaven with you
> if the cast is invalid -- dynamic_cast will give you NULL which you can
> check, static_cast will skip that check and give you a valid but
> nonsense pointer, which will most likely lead to crash).
>
> The pointer is always exactly the same. You can try pointer comparison
> on some data member:
>
> FrictPhys* fp=static_cast<FrictPhys*>(i->interactionPhysics.get());
> NormShearPhys* nsp=static_cast<NormShearPhys*>(i->interactionPhysics.get())
> assert(&(fp->shearForce)==&(nsp->shearForce));
>
> (When you access shearForce, internally you access the NormShearPhys
> where it is declared; it is the compiler's job to resolve that).
>
> HTH, Vaclav
>

Thanks for explanation! Sorry for basic question. I knew about inheritance I
didn't about static cast. I see it might also be quite dangerous.
cheers, Chiara

>
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