program structure callback

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Hi there

i have a basic question about program structure. I want to write a node that calls the laser_assembler service and publishes those scans witch have been taken during one tilt motion of my servo motor. To do so i thought of subscribing to the motor state msg the motor service publishes. How would you structure this node. Would you bind all the objects that are needed (service client, publisher ...) to the callback? Or would you write a class for this (witch would be basically my whole node). Or is it ok to have a couple of global variables?

thanks Alex