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diff --git a/libs/pbd/pbd/property_basics.h b/libs/pbd/pbd/property_basics.h
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+/*
+    Copyright (C) 2010 Paul Davis
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#ifndef __libpbd_property_basics_h__
+#define __libpbd_property_basics_h__
+
+#include <glib.h>
+#include <set>
+
+#include "pbd/xml++.h"
+
+namespace PBD {
+
+class PropertyList;
+typedef GQuark PropertyID;
+
+template<typename T>
+struct PropertyDescriptor {
+    PropertyDescriptor () : property_id (0) {}
+    PropertyDescriptor (PropertyID pid) : property_id (pid) {}
+
+    PropertyID property_id;
+    typedef T value_type;
+};
+
+class PropertyChange : public std::set<PropertyID>
+{
+public:
+	PropertyChange() {}
+
+	template<typename T> PropertyChange(PropertyDescriptor<T> p);
+
+	PropertyChange(const PropertyChange& other) : std::set<PropertyID> (other) {}
+
+	PropertyChange operator=(const PropertyChange& other) {
+		clear ();
+		insert (other.begin (), other.end ());
+		return *this;
+	}
+
+	template<typename T> PropertyChange operator=(PropertyDescriptor<T> p);
+	template<typename T> bool contains (PropertyDescriptor<T> p) const;
+
+	bool contains (const PropertyChange& other) const {
+		for (const_iterator x = other.begin (); x != other.end (); ++x) {
+			if (find (*x) != end ()) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	void add (PropertyID id)               { insert (id); }
+	void add (const PropertyChange& other) { insert (other.begin (), other.end ()); }
+	template<typename T> void add (PropertyDescriptor<T> p);
+};
+
+/** Base (non template) part of Property */
+class PropertyBase
+{
+public:
+	PropertyBase (PropertyID pid)
+		: _property_id (pid)
+		, _have_old (false)
+	{}
+
+	/** Forget about any old value for this state */
+	virtual void clear_history () {
+		_have_old = false;
+	}
+
+	virtual void add_history_state (XMLNode*)        const = 0;
+	virtual void diff (PropertyList&, PropertyList&) const = 0;
+        
+        virtual PropertyBase* maybe_clone_self_if_found_in_history_node (const XMLNode&) const { return 0; }
+
+	virtual bool set_state_from_owner_state (XMLNode const&) = 0;
+	virtual void add_state_to_owner_state (XMLNode&) const   = 0;
+
+	const gchar*property_name () const { return g_quark_to_string (_property_id); }
+	PropertyID  property_id () const   { return _property_id; }
+
+	bool operator==(PropertyID pid) const {
+		return _property_id == pid;
+	}
+
+protected:
+	PropertyID _property_id;
+	bool       _have_old;
+};
+
+class PropertyFactory 
+{
+  public:
+        static PropertyBase* create (const XMLNode&);
+};
+
+}
+
+#endif /* __libpbd_property_basics_h__ */