Is there a way to force a C# class to implement certain static functions?

No, there is no language support for this in C#. There are two workarounds that I can think of immediately:

• use reflection at runtime; crossed fingers and hope...
• use a singleton / default-instance / similar to implement an interface that declares the methods

(update)

Actually, as long as you have unit-testing, the first option isn't actually as bad as you might think if (like me) you come from a strict "static typing" background. The fact is; it works fine in dynamic languages. And indeed, this is exactly how my generic operators code works - it hopes you have the static operators. At runtime, if you don't, it will laugh at you in a suitably mocking tone... but it can't check at compile-time.

No. Basically it sounds like you're after a sort of "static polymorphism". That doesn't exist in C#, although I've suggested a sort of "static interface" notion which could be useful in terms of generics.

One thing you could do is write a simple unit test to verify that all of the types in a particular assembly obey your rules. If other developers will also be implementing the interface, you could put that test code into some common place so that everyone implementing the interface can easily test their own assemblies.

This is a great question and one that I've encountered in my projects.

Some people hold that interfaces and abstract classes exist for polymorphism only, not for forcing types to implement certain methods. Personally, I consider polymorphism a primary use case, and forced implementation a secondary. I do use the forced implementation technique fairly often. Typically, it appears in framework code implementing a template pattern. The base/template class encapsulates some complex idea, and subclasses provide numerous variations by implementing the abstract methods. One pragmatic benefit is that the abstract methods provide guidance to other developers implementing the subclasses. Visual Studio even has the ability to stub the methods out for you. This is especially helpful when a maintenance developer needs to add a new subclass months or years later.

The downside is that there is no specific support for some of these template scenarios in C#. Static methods are one. Another one is constructors; ideally, ISerializable should force the developer to implement the protected serialization constructor.

The easiest approach probably is (as suggested earlier) to use an automated test to check that the static method is implemented on the desired types. Another viable idea already mentioned is to implement a static analysis rule.

A third option is to use an Aspect-Oriented Programming framework such as PostSharp. PostSharp supports compile-time validation of aspects. You can write .NET code that reflects over the assembly at compile time, generating arbitrary warnings and errors. Usually, you do this to validate that an aspect usage is appropriate, but I don't see why you couldn't use it for validating template rules as well.