Re: Casting question

You're returning a B[] cast as an A[]. We need to return an A[] filled with 
derived type B (and then cast it to B[]). That is, create an A[] and then 
iterate through it and fill it with new Bs.

My solution doesn't do quite that, but instead allows you to specify the 
desired result type, a la ArrayList.ToArray(Type) (and incidentally, .Net 
Reflector rocks :) )

-------------- Original message --------------

> I still don't get what is the problem. If your A[] array only contains B
> objects, then you can cast it to a B[] array. I tried it here and it worked:
>
> public static A[] Gimme(int i)
> {
> A[] a = new B[i];
> return a;
> }
>
> public static void Test()
> {
> B[] b = (B[])Gimme(5); // invalid cast -> not anymore
> }
>
> There is no need for a casting operator A[] to B[]. If in fact your real
> life array has something else beside Bs (let's say that it also contains Cs,
> where C is directly derived from A and not from B) you will bump into the
> same issue because you will not be able to cast C objects to a B reference.
>
> -----Original Message-----
> From: Discussion relating to the specifics of the C# and Managed C++
> languages [mailto:DOTNET-CX@xxxxxxxxxxxxxxxxxxx]On Behalf Of Rick Taylor
> Sent: Monday, September 26, 2005 3:09 PM
> To: DOTNET-CX@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [DOTNET-CX] Casting question
>
>
> right, caught that - but, it is correct. the function is really returning an
> A[], and should, but each element in the array is a B.
>
> -------------- Original message --------------
>
> > Rick,
> >
> > Maybe in real life you do create objects of derived type(s) (B, C, D or L)
> > and store them in an array of refrences to the base type (A) but not in
> the
> > example you sent us.
> > Change the code for your Gimme method like this:
> >
> > public static A[] Gimme(int i)
> > {
> > // instead of
> > // A[] a = new A[i];
> > // have this
> > A[] a = new B[i];
> > return a;
> > }
> >
> > and you will not get the exception anymore.
> >
> > Cheers,
> > Eddie
> >
> > -----Original Message-----
> > From: Discussion relating to the specifics of the C# and Managed C++
> > languages [mailto:DOTNET-CX@xxxxxxxxxxxxxxxxxxx]On Behalf Of Rick Taylor
> > Sent: Monday, September 26, 2005 2:33 PM
> > To: DOTNET-CX@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [DOTNET-CX] Casting question
> >
> >
> > no..
> >
> > in the real life example, there are multiple types that derive from A. In
> > the scenario we are really working on, we know that the equivcalent of
> > Gimme() always returns an array of B objects for this particular case --
> > although because under other circumstances it returns C, D, and L, the
> > method signature for Gimme() remains
> >
> > public static A[] Gimme(int i)
> > (ie, returns A[] so it can fit all its target cases)
> > Assume that what comes back from Gimme() is an array of A, where every A
> in
> > the array is really a B.
> > -------------- Original message --------------
> >
> > > A is the base class and B is the derived one. You create an array of
> base
> > > objects and expect to cast them to derived ones. If you replace the
> > classes
> > > like this (which may have been your initial intention) everything is
> fine:
> > >
> > > public class B { }
> > > public class A : B { }
> > >
> > > HTH,
> > > Eddie
> > >
> > > -----Original Message-----
> > > From: Discussion relating to the specifics of the C# and Managed C++
> > > languages [mailto:DOTNET-CX@xxxxxxxxxxxxxxxxxxx]On Behalf Of Rick Taylor
> > > Sent: Monday, September 26, 2005 1:50 PM
> > > To: DOTNET-CX@xxxxxxxxxxxxxxxxxxx
> > > Subject: [DOTNET-CX] Casting question
> > >
> > >
> > > I feel like this should be obvious, but, why is the cast in Test()
> > invalid?
> > > This compiles but throws an exception. (sorry about the format, comcast
> > web
> > > interface throwing things off)
> > >
> > > public class A { }
> > > public class B : A { }
> > > public class Tester
> > > {
> > > public static A[] Gimme(int i)
> > > {
> > > A[] a = new A[i];
> > > return a;
> > > }
> > >
> > > public static void Test()
> > > {
> > > B[] b = (B[])Gimme(5); // invalid cast
> > > }
> > > }
> > >
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