Re: Polymorphism question

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Robert O asks

<<> Now I have a procedure P2 defined for type C. For type D I want to
> overload this procedure. But in the overloaded procedure I want make a
> call to P2 as defined for C, if possible without loosing the information
> that the object is actually of type D inside the called procedure.>>

To which Kirk gave the helpful :-) answer that loosing was misspelled.

But I suspect the help that Robert was looking for was how to make a call
to P2! This is easily done, just convert the argument to type C, so the
call looks like P2 (C (Arg)). This is a view conversion and indeed it
does not lose (or loose) the information that the object is actually of
type D. 

P.S. Kirk, it's a perfectly reasonable question. It might be easily assumed
that a conversion of the D object to type C would lose the tag (i.e. that
the result of the conversion would be a real C), but it is an important
part of the design that such conversions are NOT real conversions in this
sense, but simply provide a view of the D that looks like a C for the
purpose of the call, but a subsquent dispatching call will know that it
is really a D.

I hope I am correctly understanding both questions here!