Well, without the extension method language feature, you'd have to use the decorator pattern. If you only want to add a single method, that's potentially an awful lot of work, which is why I like extensions.dahat said:> If you want to add a method to a class, then subclass it.spivonious said:*snip*
What if the class you want to add a method to is sealed or worse, is a struct, preventing you from doing just that? Not unlike DateTime, TimeSpan or String?
For me the real strength of extension methods is in adding type-inferenced extension methods to interface, so that classes inheriting that interface automatically get interface-related functionality for free (we discussed this a while ago over on this thread).