[Rock-dev] accessing ports in syskit compositions via services

[Sylvain Joyeux]

On 06/25/2013 04:47 PM, Felix Rehrmann wrote:
> And now, I just wanted to know if there is a way, that is more straight 
> forward to use the abstraction
Currently, no. I've fixed the task scripting support to work at the
abstraction level, and was thinking that the data_reader / data_writer
accessors should work that way as well. I'll push it to master as soon
as next is ready.

The result will be that you can do:

class RotateTo < Syskit::Composition

     add Base::Motion2DControlledSystemSrv, :as => 'system'
     add Base::OrientationSrv, :as => 'orientation'

     argument :target_angle, :default => 0.0
     argument :rate, :default => 0.1

     script do
       reader = orientation_child.orientation_samples_port.reader
       poll do
         if value = reader.read_new 
         end
       end
     end
end

The technical issue here is that we can't make _child return
_child.as(expected_service), as it would break Roby. As far as I could
tell, we can do that only on contexts that are not accessing the Roby
API directly (i.e. the task scripting).

I'm open for suggestions, though, as I agree that it would be more intuitive

Sylvain