fix ever increasing MIDI event IDs

Iterating over a const Midi-Sequence calls Evoral::Sequence::set_event(),
which in turn used Evoral::Event::operator=()  which always created
a new event-ID (create copy of the event).

Issues fixed:
 - Saving *unmodified* MIDI produced new event-IDs on every save;
   files changed with every save. - greetings to Deva.
 - all [GUI] operations that use IDs to refer to notes e.g. undo.
   invalid undo-history.

Also clarify assignment operator name. Prefer explicit assign() over =.

2 files changed, 17 insertions, 18 deletions

diff --git a/libs/evoral/src/Event.cpp b/libs/evoral/src/Event.cpp
index 45935ccf8d..680f488596 100644
--- a/libs/evoral/src/Event.cpp
+++ b/libs/evoral/src/Event.cpp
@@ -107,30 +107,29 @@ Event<Timestamp>::~Event() {
 }
 
 template<typename Timestamp>
-const Event<Timestamp>&
-Event<Timestamp>::operator=(const Event& copy)
+void
+Event<Timestamp>::assign(const Event& other)
 {
-	_id = next_event_id ();
-	_type = copy._type;
-	_original_time = copy._original_time;
-	_nominal_time = copy._nominal_time;
-	_owns_buf = copy._owns_buf;
+	_id = other._id;
+	_type = other._type;
+	_original_time = other._original_time;
+	_nominal_time = other._nominal_time;
+	_owns_buf = other._owns_buf;
 	if (_owns_buf) {
-		if (copy._buf) {
-			if (copy._size > _size) {
-				_buf = (uint8_t*)::realloc(_buf, copy._size);
+		if (other._buf) {
+			if (other._size > _size) {
+				_buf = (uint8_t*)::realloc(_buf, other._size);
 			}
-			memcpy(_buf, copy._buf, copy._size);
+			memcpy(_buf, other._buf, other._size);
 		} else {
 			free(_buf);
 			_buf = NULL;
 		}
 	} else {
-		_buf = copy._buf;
+		_buf = other._buf;
 	}
 
-	_size = copy._size;
-	return *this;
+	_size = other._size;
 }
 
 template<typename Timestamp>
diff --git a/libs/evoral/src/Sequence.cpp b/libs/evoral/src/Sequence.cpp
index e153cea9b4..526256bf5e 100644
--- a/libs/evoral/src/Sequence.cpp
+++ b/libs/evoral/src/Sequence.cpp
@@ -284,18 +284,18 @@ Sequence<Time>::const_iterator::set_event()
 	switch (_type) {
 	case NOTE_ON:
 		DEBUG_TRACE(DEBUG::Sequence, "iterator = note on\n");
-		*_event = (*_note_iter)->on_event();
+		_event->assign ((*_note_iter)->on_event());
 		_active_notes.push(*_note_iter);
 		break;
 	case NOTE_OFF:
 		DEBUG_TRACE(DEBUG::Sequence, "iterator = note off\n");
 		assert(!_active_notes.empty());
-		*_event = _active_notes.top()->off_event();
+		_event->assign (_active_notes.top()->off_event());
 		// We don't pop the active note until we increment past it
 		break;
 	case SYSEX:
 		DEBUG_TRACE(DEBUG::Sequence, "iterator = sysex\n");
-		*_event = *(*_sysex_iter);
+		_event->assign (*(*_sysex_iter));
 		break;
 	case CONTROL:
 		DEBUG_TRACE(DEBUG::Sequence, "iterator = control\n");
@@ -303,7 +303,7 @@ Sequence<Time>::const_iterator::set_event()
 		break;
 	case PATCH_CHANGE:
 		DEBUG_TRACE(DEBUG::Sequence, "iterator = program change\n");
-		*_event = (*_patch_change_iter)->message (_active_patch_change_message);
+		_event->assign ((*_patch_change_iter)->message (_active_patch_change_message));
 		break;
 	default:
 		_is_end = true;