On Tue, Mar 23, 2010 at 8:49 AM, Radu Bogdan Rusu <rusu@willowgarage.com> wrote:

Though _not_ recommended, and if you really _cannot_ define multiple message types and multiple topics, _and_ if you
only get one of the two types of messages for the entire duration while your node is up, you can get rid of the flag,
and just subscribe to the same topic twice using different callbacks and different message types. The callback that
answers first should invalidate the other. You can see an example of this working in point_cloud_converter.

If this works it's only by accident, and is not guaranteed to work in the future. I strongly recommend you don't rely on it (including in point_cloud_converter).

Actually, a quick test shows that it does not work (first subscription wins) so relying on it is definitely a bad idea.

Josh