Question on Interface.

[SteveGuo]

> if D would allow this - what is then the difference between a 
> class with your methods as virtuals + your string?
>
> interface are for loosier coupling then classes - thats why 
> only declerations not implementations (like your string) are 
> allowed, same goes to Java and C# (and i think most other 
> interface having languages)

But classes cannot enforce its successor to do something. May 
introduce a new keyword "enforce"?