import System class Point(ValueType): public X as int public Y as int class Point3D: public xy as Point public Z as int p = Point3D() print p.xy.X System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.TypeLoadException: Could not load type Point from assembly untitled, Version=0.0.0.0. at UntitledModule.Main(String[] argv) — End of inner exception stack trace — at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean verifyAccess) at System.Reflection.RuntimeMethodInfo.InternalInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean verifyAccess) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at BooExplorer.BooEditor.Run() in I:\Boo\booTrunk\extras\boox\booxw\src\BooEditor.boo:line 221