if (item is MyDerivedGenericClass<>)  // Won't compile

public interface MarkerA { }  // Empty Interface
public interface MarkerB { }  // Empty Interface
public interface MarkerC { }  // Empty Interface

public class BaseClass { }

public class DerivedClassA : BaseClass { }
public class DerivedClassB : BaseClass { }
public class DerivedClassC : BaseClass { }

public class DerivedSpecialClass : BaseClass { }

public class DerivedSpecialA : DerivedSpecialClass { }
public class DerivedSpecialB : DerivedSpecialClass { }
public class DerivedSpecialC : DerivedSpecialClass { }

public class DerivedSpecialGenericA<T> : DerivedSpecialClass, MarkerA { }
public class DerivedSpecialGenericB<T> : DerivedSpecialClass, MarkerB { }
public class DerivedSpecialGenericC<T> : DerivedSpecialClass, MarkerC { }


public void ProcessClasses(List<BaseClass> list)
    {
        // Iterate through a list of mixed classes that all derive from BaseClass
        foreach (BaseClass item in list)
        {

            // Ideal approach, but doesn't compile:

            // Try to isolate select class types to do something interesting with
            if ((item is DerivedSpecialA) || (item is DerivedSpecialB) || (item is DerivedSpecialGenericB<>))
            {
                var specialItem = item as DerivedSpecialClass;

                DoSomethingInteresting(specialItem);

                Console.WriteLine(specialItem.Title);
            }


            // Alternative workaround that tests for the Marker instead

            // Try to isolate select class types to do something interesting with
            if ((item is DerivedSpecialA) || (item is DerivedSpecialB ) || (item is MarkerB))
            {
                var specialItem = item as DerivedSpecialClass;

                DoSomethingInteresting(specialItem);

                Console.WriteLine(specialItem.Title);
            }
        }
    }

public class BaseClass
{
    public abstract MarkerType { get; }
}

public enum MarkerType { A, B, C }