Is there a standard way to store state to build messages from separate submessages published on different topics at different times?

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Say message A depends on information from independently published messages B and C, posted on separate topics at different rates (example, a dilution of precision measurement and a position measurement from a gps sensor are combined to produce a NavSatFix message with both the position and the calculated accuracy of that position). This implies that either message B or message C must be stored and re-accessed after it is published and received in order to compose and publish message A.

Is there a standard way in ROS to handle situations like this?w Topics are a Pub/Sub event model that relies on fire and forget to be performant. Services are supposed to perform as transformation functions over their inputs without storing intermediate values and would make sense to do the job of transforming message B and C into message A after being passed B and C. However, B and C arrive independently.

tf appears to have a means of performing timed polling of a message on its topic. Is this capability built into all topics? Additionally, I'd like to access only the "latest" message rather than a message at a specific time point in the past. That ability does not seem to be built into tf, and so I would assume it isn't in other topic/msg based interfaces either.

I considered using rosbag, but I would prefer to not rely on storing items on the filesystem if possible, and it too appears to be able to only read messages at a specifed time, rather than the latest available message.

As a last resort, I have constructed my own message cache using a ring buffer and numpy arrays to store the messages. I'd prefer a standard solution if it exists.