using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication7
{
    interface IClass<T>
    {

    }

    class Class1<T> : IClass<T>
    {

    }

    class Class2<T> : IClass<T>
    {

    }

    class Class3 : IClass<int>
    {

    }

    class Program
    {
        static void Main(string[] args)
        {
            // only prints Class3
            foreach (var type in GetClosedGenericSubClasses<int>())
            {
                Console.WriteLine(type.FullName);
            }
        }

        static IEnumerable<Type> GetClosedGenericSubClasses<U>()
        {

            return Assembly.GetExecutingAssembly().GetTypes().Where(type => typeof(IClass<U>).IsAssignableFrom(type));
            //return Assembly.GetExecutingAssembly().GetTypes().Where(type => type.IsSubclassOf(typeof(IClass<U>)));
        }
    }
}