Putting a base in the middle
- by PSteele
From Eric Lippert's Blog: Here’s a crazy-seeming but honest-to-goodness real customer scenario that got reported to me recently. There are three DLLs involved, Alpha.DLL, Bravo.DLL and Charlie.DLL. The classes in each are: public class Alpha // In Alpha.DLL { public virtual void M() { Console.WriteLine("Alpha"); } } public class Bravo: Alpha // In Bravo.DLL { } public class Charlie : Bravo // In Charlie.DLL { public override void M() { Console.WriteLine("Charlie"); base.M(); } } Perfectly sensible. You call M on an instance of Charlie and it says “Charlie / Alpha”. Now the vendor who supplies Bravo.DLL ships a new version which has this code: public class Bravo: Alpha { public override void M() { Console.WriteLine("Bravo"); base.M(); } } The question is: what happens if you call Charlie.M without recompiling Charlie.DLL, but you are loading the new version of Bravo.DLL? The customer was quite surprised that the output is still “Charlie / Alpha”, not “Charlie / Bravo / Alpha”. Read the full post for a very interesting discussion of the design of C#, the CLR, method resolution and more. Technorati Tags: .NET,C#,CLR
