This block samples the signal at its input and packs it into a ROS message of type std_msgs::Float64. Each time the block is run by its time domain, this message is published under a given topic name.

  RosPublisherDouble pubDouble("myTopic"); // create publisher block

For ROS2 you have to pass the node, from where the topic is sent. The ROS2 message is of type std_msgs::msg::Float64.

  RosPublisherDouble pubDouble(node, "myTopic"); // create publisher block

This block can be connected to any signal whose value has type double.
The time stamp of the signal is not transmitted.