Extension interface patterns

Question

The new extensions in .Net 3.5 allow functionality to be split out from interfaces.

For instance in .Net 2.0

public interface IHaveChildren {
    str         


        

Answer 1

Extension methods should be used as just that: extensions. Any crucial structure/design related code or non-trivial operation should be put in an object that is composed into/inherited from a class or interface.

Once another object tries to use the extended one, they won't see the extensions and might have to reimplement/re-reference them again.

The traditional wisdom is that Extension methods should only be used for:

• utility classes, as Vaibhav mentioned
• extending sealed 3rd party APIs