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

[Jean-Pierre D. <jea...@tr...>]

Jim,

In fact you used the technique yourself in "EXAMPLE - Get Obj Info From R=
ef.vi" and that made me post the message about "Class
Downcast to Self.vi". This VI should indeed check if the object is valid =
and return an error for invalid object even if the class
downcast succeeds.

Jean-Pierre


----- Message d'origine -----=20
De : "Jim Kring" <ji...@ji...>
=C0 : <ope...@li...>
Envoy=E9 : 13 octobre, 2003 20:28
Objet : [opengoop] "Variant To Data" downcasts Class Type Inheritance Ref=
nums


> Based on Jean-Pierre's comments about using "Variant to Data" for downc=
asting
> an inheritable data structure, I realized that "Variant to Data" can be=
 used
> for downcasting Class Type Inheritance Refnums (analagous to "To More
> Specific Class" fuction).  It will even output an error at run-time (Er=
ror
> 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 tha=
t a class
> does not have to provide a polymorphic VI for downcasting to each desce=
ndant
> type.  The only downside, is that this method does not rely on the obje=
ct
> reference to check if the object is really of the more specific type.
> However, this check will have to be done in any downstream VI that oper=
ates
> on the more specific type.
>
> -Jim
>
>
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