Re: Use 'new' keyword...

Following up on this (after looking over the MSDN articles on new and
override), it seems that I will have to use the 'new' keyword - at least I
can't get the override modifier to work.  For the case of the 'Copy' method
on the smaller object A, it returns an object of type A.  B's 'Copy' method
is supposed to return an object of type B.  If I declare the 'Copy' method
in A as virtual (so that B can override it), B.Copy will also need to return
an object of type A (since that's what A's overridden method returned).
Therefore, it seems I must use the 'new' keyword.

Or did I misunderstand?

Peter

> -----Original Message-----
> From: Discussion relating to the specifics of the C# and
> Managed C++ languages [mailto:[email protected]]
> On Behalf Of Peter Osucha
> Sent: Thursday, November 02, 2006 3:28 PM
> To: [email protected]
> Subject: Re: [DOTNET-CX] Use 'new' keyword...
>
> > You probably already know this, but just in case you don't:
> > you should also think about if "new" is really the right choice. In
> > practice, "new" means your objects will have two methods of
> the same
> > name (and parameter lists), which can be confusing.
> >
> > Consider this:
> > B b1 = new B();
> > A b2 = new B(); // this works because B is a subclass of A
> >
> > b1.Copy(); // calls B's Copy -> returns a new B object, a
> copy of b1
> > b2.Copy(); // calls A's Copy -> returns a new A object, a
> copy of the
> > "A part" of b2
>
> Hold on - this one has me confused.  In my example, A is the 'smaller'
> object.  B is (essentially) A with a few more properties
> (it's base is A).
> I would think it is the other way.  I could create...
>
> A first = new A();
> B second = new A();
>
> But I can't do...
>
> A third = new B();
> B fourth = new B();
>
> Because the line with 'third' above would fail, right?
>
> > In most cases, you actually want to use override instead of new, so
> > that B's Copy method replaces the one defined by A, and
> b2.Copy will
> > correctly create a full-featured B object as well.
> >
> > In those cases, where override is not what you want, you
> should think
> > about using different names for the different methods.
>
> Override is exactly what I want here.  That way, if B's
> 'Copy' method is used, it creates an exact copy of the full
> featured B object. (Thanks!)
>
> > (Side note: The .NET framework uses the term "cloning" for making
> > copies of objects. There's also an interface ICloneable that
> > can/should be implemented by objects that support being cloned.)
>
> I did realize this.  I haven't done much to attempt to
> implement Icloneable for these objects.  I purposely used the
> method name 'Copy' here instead of 'Clone' because (be it a
> good reason or a bad), I wanted to separate - in my head at
> least - that I was manually copying the object to create a
> new one instead of implementing the Icloneable interface.
>
> Peter

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