Re: Use 'new' keyword...

> 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.

It will be declared to return an instance of type A, but since B isa
A, an instance of B can actually be returned from B's Copy() and
things will be just fine.  In an instance where you KNOW that you are
expecting a B, it's safe to up-cast the returned value as needed.

Think this:

public class A
{
   public virtual A Copy() { return new A(); }
   public void Who() { Console.WriteLine(this.GetType().Name); }
}

public class B : class A
{
   public override A Copy() { return new B(); }
}

public class Program
{
   static int Main()
   {
      A a = new A();
      a.Who();
      A b = a.Copy();
      b.Who();
      B c = new B();
      b.Who();
      A d = b.Copy();
      d.Who();
      B e = (B)d.Copy();
      e.Who();
   }
}

Will print (ignoring any namespace...)
A
A
B
B
B

If it confuses you to think this is "safe", just substitute "object"
for A in the declarations mentally and see how that mirror nomal
use...

--
"We do not have the luxury of making that risky assumption that people
will not be affected by the potential change. I know this can be
frustrating for you as it is for us. Thanks for your understanding in
this matter.." --Some misguided soul at Microsoft

Marc C. Brooks
http://musingmarc.blogspot.com

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