add get/set state methods to TimeDomainProvider

These are not used yet, because only the Session really acts as a Provider
and it uses the Config::default_time_domain to serialize that state

libs/temporal/domain.cc

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2023 Paul Davis <paul@linuxaudiosystems.com>
+ *
+ * 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.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "temporal/domain_provider.h"
+#include "temporal/types_convert.h"
+
+#include "pbd/i18n.h"
+
+using namespace Temporal;
+
+XMLNode&
+TimeDomainProvider::get_state () const
+{
+	XMLNode* node = new XMLNode (X_("TimeDomainProvider"));
+	node->set_property (X_("has-own"), have_domain);
+	if (have_domain) {
+		node->set_property (X_("domain"), domain);
+	}
+	return *node;
+}
+
+int
+TimeDomainProvider::set_state (const XMLNode& node, int version)
+{
+	node.get_property (X_("has-own"), have_domain);
+	if (have_domain) {
+		node.get_property (X_("domain"), domain);
+	}
+	return 0;
+}
+

libs/temporal/temporal/domain_provider.h

@@ -20,11 +20,13 @@
 #define __temporal_domain_provider_h__
 
 #include "pbd/signals.h"
+#include "pbd/stateful.h"
+
 #include "temporal/types.h"
 
 namespace Temporal {
 
-class TimeDomainProvider {
+class TimeDomainProvider  {
   public:
 	explicit TimeDomainProvider () : have_domain (false), parent (nullptr) {}
 	explicit TimeDomainProvider (TimeDomain td) : have_domain (true), domain (td), parent (nullptr) {}
@@ -38,6 +40,11 @@ class TimeDomainProvider {
 
 	virtual ~TimeDomainProvider() {}
 
+	/* replicates part of Stateful API but we do not want inheritance */
+
+	XMLNode& get_state () const;
+	int set_state (const XMLNode&, int version);
+
 	TimeDomainProvider& operator= (TimeDomainProvider const & other) {
 		if (this != &other) {
 			parent_connection.disconnect ();

libs/temporal/wscript

@@ -28,6 +28,7 @@ temporal_sources = [
     'debug.cc',
     'bbt_time.cc',
     'beats.cc',
+    'domain.cc',
     'enums.cc',
     'range.cc',
     'superclock.cc',