Creating an array/list of existing message type without defining custom message type?
Is there a way to create an array of an existing message type without defining another message type?
As a use-case, say you have many .bag files, each with a username. You compile them into a summary bag file and would like all unique usernames in a metadata topic for convenience. Is there any way to accomplish something like this without a custom message type?
users = get_unique_users() # a function returns a list of strings: [user1, user2, ..., userN]
outbag = rosbag.Bag('/path/to/file.bag', 'w')
outbag.write('/metadata/unique_users', std_msgs.msg.String(users))
It seems that an array of an existing message is such a simple extension that I'd figure such a mechanism exists. My current approach was to create a new package, std_msgs_array with:
$ rosmsg show std_msgs_array/StringArray
string[] data
$ rosmsg show std_msgs_array/Float64Array
float64[] data
Is this expected or am I overlooking something? I do note the following from the ROS Wiki:
...it's usually "better" (in the sense of making the code easier to understand, etc.) when developers use or create non-generic message types
Perhaps the intention is to force more project-specific message creation rather than relying on built-in, canned examples. This use-case might be somewhat fringe where I truly am looking for a "throwaway"; all I care about is getting a list of very basic values into the output .bag vs. something like sensor data specific to a more complicated process.
