Return a ROSClock from Clock constructor if appropriate

rclpy/rclpy/clock.py

@@ -31,11 +31,16 @@ class ClockType(IntEnum):
 
 class Clock:
 
-    def __init__(self, *, clock_type=ClockType.SYSTEM_TIME):
+    def __new__(cls, *, clock_type=ClockType.SYSTEM_TIME):
         if not isinstance(clock_type, ClockType):
             raise TypeError('Clock type must be a ClockType enum')
+        if clock_type is ClockType.ROS_TIME:
+            self = super().__new__(ROSClock)
+        else:
+            self = super().__new__(cls)
         self._clock_handle = _rclpy.rclpy_create_clock(clock_type)
         self._clock_type = clock_type
+        return self
 
     @property
     def clock_type(self):
@@ -55,9 +60,6 @@ def now(self):
 
 class ROSClock(Clock):
 
-    def __init__(self):
-        super(ROSClock, self).__init__(clock_type=ClockType.ROS_TIME)
-
     @property
     def ros_time_is_active(self):
         return _rclpy.rclpy_clock_get_ros_time_override_is_enabled(self._clock_handle)

rclpy/rclpy/time_source.py

@@ -13,8 +13,6 @@
 # limitations under the License.
 
 import builtin_interfaces.msg
-from rclpy.clock import Clock
-from rclpy.clock import ClockType
 from rclpy.clock import ROSClock
 from rclpy.time import Time
 
@@ -73,12 +71,8 @@ def detach_node(self):
         self._node = None
 
     def attach_clock(self, clock):
-        if not isinstance(clock, Clock):
-            raise TypeError('Clock must be of type rclpy.clock.Clock')
-        if not clock.clock_type == ClockType.ROS_TIME:
+        if not isinstance(clock, ROSClock):
             raise ValueError('Only clocks with type ROS_TIME can be attached.')
-        # "Cast" to ROSClock subclass so ROS time methods can be used.
-        clock.__class__ = ROSClock
         if self._last_time_set is not None:
             self._set_clock(self._last_time_set, clock)
         clock._set_ros_time_is_active(self.ros_time_is_active)

rclpy/test/test_clock.py

@@ -17,6 +17,7 @@
 
 from rclpy.clock import Clock
 from rclpy.clock import ClockType
+from rclpy.clock import ROSClock
 from rclpy.time import Time
 
 
@@ -28,12 +29,14 @@ def test_clock_construction(self):
         with self.assertRaises(TypeError):
             clock = Clock(clock_type='STEADY_TIME')
 
-        clock = Clock(clock_type=ClockType.ROS_TIME)
-        assert clock.clock_type == ClockType.ROS_TIME
         clock = Clock(clock_type=ClockType.STEADY_TIME)
         assert clock.clock_type == ClockType.STEADY_TIME
         clock = Clock(clock_type=ClockType.SYSTEM_TIME)
         assert clock.clock_type == ClockType.SYSTEM_TIME
+        # A subclass ROSClock is returned if ROS_TIME is specified.
+        clock = Clock(clock_type=ClockType.ROS_TIME)
+        assert clock.clock_type == ClockType.ROS_TIME
+        assert isinstance(clock, ROSClock)
 
     def test_clock_now(self):
         # System time should be roughly equal to time.time()

rclpy/test/test_time_source.py

@@ -53,11 +53,7 @@ def test_time_source_attach_clock(self):
         # ROSClock is a specialization of Clock with ROS time methods.
         time_source.attach_clock(ROSClock())
 
-        # A clock of type ROS_TIME can be attached. It will be converted to a ROSClock for storage.
-        time_source.attach_clock(Clock(clock_type=ClockType.ROS_TIME))
-
-        assert all((isinstance(clock, ROSClock) for clock in time_source._associated_clocks))
-
+        # Other clock types are not supported.
         with self.assertRaises(ValueError):
             time_source.attach_clock(Clock(clock_type=ClockType.SYSTEM_TIME))