+ DECLARE_SCHEME_CALLBACK(constructor, ());
+ DECLARE_SCHEME_CALLBACK(once_finalization, (SCM, SCM ));
+
+protected:
+ virtual void do_quit();
+ virtual void process (Moment);
+};
+
+
+
+
+/**
+ Iterate a property.
+ */
+class Property_unset_iterator : public Simple_music_iterator
+{
+public:
+ DECLARE_SCHEME_CALLBACK(constructor, ());