simple assignment of callback
simple assignment of callback

halfflat/arbor,halfflat/nestmc-proto,eth-cscs/nestmc-proto,halfflat/arbor,eth-cscs/nestmc-proto,halfflat/arbor,halfflat/nestmc-proto,eth-cscs/nestmc-proto,halfflat/arbor,halfflat/nestmc-proto,halfflat/arbor