How to determine if a type implements a specific generic interface type

As a helper method extension

public static bool Implements<I>(this Type type, I @interface) where I : class
{
    if(((@interface as Type)==null) || !(@interface as Type).IsInterface)
        throw new ArgumentException("Only interfaces can be 'implemented'.");

    return (@interface as Type).IsAssignableFrom(type);
}

Example usage:

var testObject = new Dictionary<int, object>();
result = testObject.GetType().Implements(typeof(IDictionary<int, object>)); // true!

First of all public class Foo : IFoo<T> {} does not compile because you need to specify a class instead of T, but assuming you do something like public class Foo : IFoo<SomeClass> {}

then if you do

Foo f = new Foo();
IBar<SomeClass> b = f as IBar<SomeClass>;

if(b != null)  //derives from IBar<>
    Blabla();