[ros-users] Parameter resolution order in launch files

[Patrick Bouffard]

Hi Ken,

On Mon, Dec 27, 2010 at 10:23 PM, Ken Conley <kwc at willowgarage.com> wrote:
> Good recommendation.  I added a paragraph here.  Please let me know
> what you think:
>
> http://www.ros.org/wiki/roslaunch/XML#Evaluation_order

Thanks, that looks good. One question: that paragraph seems to be
written to apply to the whole launch file, not just parameters. But
are there any other elements that can be defined more than once
without throwing an error? E.g. if you define a machine or node twice,
roslaunch yells at you doesn't it? Are you saying that the same rule
applies to <arg> tags too?

Also I'm not sure I understand what you mean by 'brittle' override
behaviour. Of course if you don't have the right parameter name the
override won't work--how would args make this any better? And wouldn't
you have to have an <arg> for every single parameter you ever want to
change? Do you just mean that if you provide an arg setting that isn't
used, that roslaunch will complain (IIRC)?

Are the ways that roslaunch will complain such as those I mentioned,
and (maybe more importantly) the cases where it won't complain,
documented somewhere?

Cheers,
Pat