Feature request

Feature description

It would be convenient to have a way to check if rclcpp::init has been called, similar to ros::isInitialized.

Implementation considerations

If this has been left out due to some design decision, I suppose users can live without it, and instead try to catch specific errors resulting from not calling init. I searched a bit and couldn't find an explanation, so I imagine it may just be in the backlog?

Thanks!