resolve merge with master (?)

[ardour.git] / libs / pbd / pbd / memento_command.h

diff --git a/libs/pbd/pbd/memento_command.h b/libs/pbd/pbd/memento_command.h
index a46aea0002cbef84ed563f694f2739086da9c9ae..45cb100a36e6d967e28771b6f935b565ad1d465e 100644 (file)
--- a/libs/pbd/pbd/memento_command.h
+++ b/libs/pbd/pbd/memento_command.h
@@ -34,20 +34,32 @@
 /** A class that can return a Stateful object which is the subject of a MementoCommand.
  *
  *  The existence of this class means that the undo record can refer to objects which
- *  don't exist in the session file.  Currently this is just used for MIDI automation;
- *  when MIDI automation is edited, undo records are written for the AutomationList being
- *  changed.  However this AutomationList is a temporary structure, built by a MidiModel,
- *  which doesn't get written to the session file.  Hence we need to be able to go from
- *  a MidiSource and Parameter to an AutomationList.  This Binder mechanism allows this
- *  through MidiAutomationListBinder; the undo record stores the source and parameter,
+ *  don't exist in the session file.  Currently this is used for
+ *
+ *  1.  MIDI automation; when MIDI automation is edited, undo records are
+ *  written for the AutomationList being changed.  However this AutomationList
+ *  is a temporary structure, built by a MidiModel, which doesn't get written
+ *  to the session file.  Hence we need to be able to go from a MidiSource and
+ *  Parameter to an AutomationList.  This Binder mechanism allows this through
+ *  MidiAutomationListBinder; the undo record stores the source and parameter,
  *  and these are bound to an AutomationList by the Binder.
+ *
+ *  2.  Crossfades; unlike regions, these are completely removed from a session
+ *  when they are deleted.  This means that the undo record can contain
+ *  references to non-existant crossfades.  To get around this, CrossfadeBinder
+ *  can do `just-in-time' binding from the crossfade ID.
  */
 template <class obj_T>
 class MementoCommandBinder : public PBD::Destructible
 {
 public:
        /** @return Stateful object to operate on */
-       virtual obj_T* get () = 0;
+       virtual obj_T* get () const = 0;
+
+       /** @return Name of our type */
+       virtual std::string type_name () const {
+               return PBD::demangled_name (*get ());
+       }
 
        /** Add our own state to an XMLNode */
        virtual void add_state (XMLNode *) = 0;
@@ -64,7 +76,7 @@ public:
                _object.Destroyed.connect_same_thread (_object_death_connection, boost::bind (&SimpleMementoCommandBinder::object_died, this));
        }
 
-       obj_T* get () {
+       obj_T* get () const {
                return &_object;
        }
 
@@ -73,6 +85,7 @@ public:
        }
        
        void object_died () {
+               /* The object we are binding died, so drop references to ourselves */
                this->drop_references ();
        }
 
@@ -92,13 +105,15 @@ public:
        MementoCommand (obj_T& a_object, XMLNode* a_before, XMLNode* a_after) 
                : _binder (new SimpleMementoCommandBinder<obj_T> (a_object)), before (a_before), after (a_after)
        {
-               _binder->Destroyed.connect_same_thread (_binder_death_connection, boost::bind (&MementoCommand::binder_died, this));
+               /* The binder's object died, so we must die */
+               _binder->DropReferences.connect_same_thread (_binder_death_connection, boost::bind (&MementoCommand::binder_dying, this));
        }
 
        MementoCommand (MementoCommandBinder<obj_T>* b, XMLNode* a_before, XMLNode* a_after) 
                : _binder (b), before (a_before), after (a_after)
        {
-               _binder->Destroyed.connect_same_thread (_binder_death_connection, boost::bind (&MementoCommand::binder_died, this));
+               /* The binder's object died, so we must die */
+               _binder->DropReferences.connect_same_thread (_binder_death_connection, boost::bind (&MementoCommand::binder_dying, this));
        }
        
        ~MementoCommand () {
@@ -108,7 +123,7 @@ public:
                delete _binder;
        }
 
-       void binder_died () {
+       void binder_dying () {
                delete this;
        }
 
@@ -137,7 +152,7 @@ public:
                XMLNode* node = new XMLNode(name);
                _binder->add_state (node);
                
-               node->add_property("type_name", demangled_name (*_binder->get()));
+               node->add_property ("type_name", _binder->type_name ());
 
                if (before) {
                        node->add_child_copy(*before);