using System;

​

public interface A

{

}

​

;

public interface B : A

{

}

​

;

public interface C : A

{

}

​

;

public interface IMyInterface<in T>

    where T : A

{

}

​

;

public class FirstImpl<T> : IMyInterface<T> where T : B

{

}

​

;

public class SecondImpl<T> : IMyInterface<T> where T : C

{

}

​

;

public class Program

{

    public static void Main()

    {

        var test1 = Create<B>();

        var test2 = Create<C>();

        Console.WriteLine("test1 " + test1.GetType().Name);

        Console.WriteLine("test2 " + test2.GetType().Name);

    }

​

    public static IMyInterface<T> Create<T>()where T : A

    {

        if (typeof (B).IsAssignableFrom(typeof (T)))

        {

            return CreateImplementation<T>(typeof (FirstImpl<>));

        }

        else if (typeof (C).IsAssignableFrom(typeof (T)))

        {

            return CreateImplementation<T>(typeof (SecondImpl<>));

        }

​

        throw new ArgumentException("unknown type " + typeof (T).Name);

    }

​

    private static IMyInterface<T> CreateImplementation<T>(Type implementationType)where T : A

    {

        var boundType = implementationType.MakeGenericType(typeof (T));

        return Activator.CreateInstance(boundType) as IMyInterface<T>;

    }

}