check for interfaces in c#

today an interesting question about interfaces came up. Does reflection's GetInterfaces() return all interfaces of all hierarchical levels?

Test-Suite:

    public interface ILevel1{}

    public interface ILevel2 : ILevel1, IAdditionalInterface2{}

    public interface ILevel3 : ILevel2{}

    public interface IAdditionalInterface {}

    public interface IAdditionalInterface2 { }

    public class MyClass : ILevel3, IAdditionalInterface {}

The answer is yes: it does!

MyClass implements any interface which can be tested using the 

• "is"-operator (INSTANCE is INTERFACE_TO_CHECK) or 
• INSTANCE.GetType().GetInterfaces().Contains(typeof( INTERFACE_TO_CHECK ))

both methods return the same.

kr,

Daniel