using System;

public interface IFoo { }

​

public interface IFooWrapper<out I> where I : IFoo { }

​

public class Foo : IFoo { }

public class FooWrapper : IFooWrapper<Foo> { }

​

class Tester 

{

    void Test()

    {

        IFooWrapper<IFoo> foo = new FooWrapper();

    }

}

​