RE: [opengoop] "Variant To Data" downcasts Class Type Inheritance Refnums

[Jim K. <ji...@ji...>]

> In fact you used the technique yourself

Ah, yes :-))

-Jim

> -----Original Message-----
> From: ope...@li...
> [mailto:ope...@li...]=20
> On Behalf Of Jean-Pierre Drolet
> Sent: Monday, October 13, 2003 6:23 PM
> To: ope...@li...
> Subject: Re: [opengoop] "Variant To Data" downcasts Class=20
> Type Inheritance Refnums
>=20
>=20
> Jim,
>=20
> In fact you used the technique yourself in "EXAMPLE - Get Obj
> Info From Ref.vi" and that made me post the message about=20
> "Class Downcast to Self.vi". This VI should indeed check if=20
> the object is valid and return an error for invalid object=20
> even if the class downcast succeeds.
>=20
> Jean-Pierre
>=20
>=20
> ----- Message d'origine -----
> De : "Jim Kring" <ji...@ji...>
> =C0 : <ope...@li...>
> Envoy=E9 : 13 octobre, 2003 20:28
> Objet : [opengoop] "Variant To Data" downcasts Class Type=20
> Inheritance Refnums
>=20
>=20
> > Based on Jean-Pierre's comments about using "Variant to Data" for
> > downcasting an inheritable data structure, I realized that=20
> "Variant to
> > Data" can be used for downcasting Class Type Inheritance Refnums
> > (analagous to "To More Specific Class" fuction).  It will=20
> even output
> > an error at run-time (Error 91, "The data type of the
> variant is not
> > compatible with the data type wired to the type input."),
> if the class
> > information in the variant does not match the more specific
> type.  For
> > example, this prevents one from trying to Downcast to a
> class from the
> > classes uncle (Car =3D=3D> DeLorian is OK, but Truck =3D=3D>
> Delorian produces
> > an ERROR).  Adopting this technique means that a class does
> not have
> > to provide a polymorphic VI for downcasting to each
> descendant type.
> > The only downside, is that this method does not rely on the object
> > reference to check if the object is really of the more=20
> specific type.
> > However, this check will have to be done in any downstream VI that
> > operates on the more specific type.
> >
> > -Jim
> >
> >
>=20
>=20
>=20