Why static classes cant implement interfaces?

Question

Possible Duplicate:
Why Doesn’t C# Allow Static Methods to Implement an Interface?

In my application I want to use a Repository that will do the raw data access (TestRepository, SqlRepository, FlatFileRepository etc). Because such a repository would be used throughout the runtime of my application it seemed like a sensible thing to me to make it a static class so I could go

SqlRepository.GetTheThingById(5);

without it having to be regenerated all the time. Because I want my repositories to be interchangeable, I want them to implement a common interface: IRepository. But when I try to do so, I get:

Static classes cannot implement interfaces

Why can't they? How do you suggest I change my design then? Is there a pattern I could use?

UPDATE
Five years later: this question is visited 20k+ times, I learned about the disadvantages of the repository pattern, learned about IoC and realise my question was poorly formulated.

I wasn't really asking what the C# specification of an interface is, rather why it was deliberately restricting me in this specific way.

The practical answer is that the syntax for calling a method on an instance or on a type are different. But the question is closed.

Answer 1

Interfaces can't have static methods. A class that implements an interface needs to implement them all as instance methods. Static classes can't have instance methods. QED.