[libsigc++2] trackable: move assignment operator: null the src.

[Murray Cumming <murrayc src gnome org>]

commit ea858520f2f3d4825942d01eeeb0b1e834aef2b1
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Sep 1 15:43:03 2015 +0200

    trackable: move assignment operator: null the src.

 sigc++/trackable.cc          |    2 +
 tests/test_trackable_move.cc |   66 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+), 0 deletions(-)
---
diff --git a/sigc++/trackable.cc b/sigc++/trackable.cc
index 83c87cb..e261697 100644
--- a/sigc++/trackable.cc
+++ b/sigc++/trackable.cc
@@ -58,6 +58,8 @@ trackable& trackable::operator=(trackable&& src)
 
   callback_list_ = std::move(src.callback_list_);
 
+  src.callback_list_ = nullptr;
+
   return *this;
 }
 
diff --git a/tests/test_trackable_move.cc b/tests/test_trackable_move.cc
new file mode 100644
index 0000000..41d7aa4
--- /dev/null
+++ b/tests/test_trackable_move.cc
@@ -0,0 +1,66 @@
+// -*- c++ -*-
+/* Copyright 2002, The libsigc++ Development Team
+ *  Assigned to public domain.  Use as you wish without restriction.
+ */
+
+#include "testutilities.h"
+#include <sstream>
+#include <cstdlib>
+#include <sigc++/trackable.h>
+#include <sigc++/functors/slot.h>
+#include <sigc++/functors/mem_fun.h>
+
+namespace
+{
+std::ostringstream result_stream;
+
+class my_class: public sigc::trackable
+{
+public:
+
+  my_class(const myclass& src) = delete;
+  my_class& operator=(const myclass& src) = delete;
+
+  my_class(myclass&& src)
+  : sigc::trackable(std::move(src)),
+    i(std::move(src.i);
+  {
+  }
+
+  my_class& operator=(myclass&& src)
+  {
+    sigc::trackable::operator=(std::move(src));
+    i = std::move(src.i);
+  }
+
+  int i;
+
+  void foo()
+  {
+    result_stream << i;
+  }
+};
+
+} // end anonymous namespace
+
+int main(int argc, char* argv[])
+{
+  auto util = TestUtilities::get_instance();
+
+  if (!util->check_command_args(argc, argv))
+    return util->get_result_and_delete_instance() ? EXIT_SUCCESS : EXIT_FAILURE;
+
+  sigc::slot<void> sl;
+  {
+    my_class t;
+    t.i = 10;
+    sl = sigc::mem_fun0(&t, &my_class::foo);
+    sl();
+    util->check_result(result_stream, "10");
+  }
+
+  sl();
+  util->check_result(result_stream, "");
+
+  return util->get_result_and_delete_instance() ? EXIT_SUCCESS : EXIT_FAILURE;
+}