When can a Duration/Time be negative? #525
Description
Spinning off from ros2/geometry2#67 (comment) so I don't hijack that thread (and so the convo doesn't get lost).
I thought that Durations could not store negative values but from @tfoote's comment it sounds like that understanding is incorrect. The source of my misunderstanding is this line:
rclcpp/rclcpp/src/rclcpp/duration.cpp
Line 92 in af6e86c
Should that check be removed? Or is it appropriate in that situation?