Is there any way in C# to override a class method with an extension method?

Question

There have been occasions where I would want to override a method in a class with an extension method. Is there any way to do that in C#?

For example:

public static class StringExtension {     public static int GetHashCode(this string inStr)     {         return MyHash(inStr);     } } 

A case where I've wanted to do this is to be able to store a hash of a string into a database and have that same value be used by all the classes that use the string class's hash (i.e. Dictionary, etc.) Since the built-in .NET hashing algorithm is not guaranteed to be compatible from one version of the framework to the next, I want to replace it with my own.

There are other cases I've run into where I'd want to override a class method with an extension method as well so it's not just specific to the string class or the GetHashCode method.

I know I could do this with subclassing off an existing class but it would be handy to be able to do it with an extension in a lot of cases.

Answer 1

No; an extension method never takes priority over an instance method with a suitable signature, and never participates in polymorphism (GetHashCode is a virtual method).

Answer 2

If the method has a different signature, then it can be done -- so in your case: no.

But otherwise you need to use inheritance to do what you are looking for.