Bug report

Required Info:

• Operating System:
  Ubuntu 16.04
• Installation type:
  • binary
• Version or commit hash:
  • rclcpp: 0.4.0-0xenial-20180208-1432
• Client library (if applicable):
  • rclcpp

Feature description

Feedback from a new ROS2 user: I think the new clock is unnecessarily confusing. Why does the constructor take seconds and nanoseconds, but there's only a method to access nanoseconds?

When I retrieve nanoseconds like so:

rclcpp::Duration delta_t_;
delta_t_.nanoseconds();

Am I getting the total time (seconds+nanoseconds)? Or is it the modulo?

My initial thought was that I should do this to convert to seconds, but I have a feeling this is not correct:
delta_t_.nanoseconds()/1000000000;