  We study the classical optics effects known as Goos-H\"anchen (GH) and
Imbert-Fedorov (IF) shifts, occurring when reflecting a bounded light beam from
a planar surface, by using a quantum-mechanical formalism. This new approach
allows us to naturally separate the spatial shift into two parts, one
independent on orbital angular momentum (OAM) and the other one showing
OAM-induced spatial-vs-angular shift mixing. In addition, within this
quantum-mechanical-like formalism, it becomes apparent that the angular shift
is proportional to the beams angular spread, namely to the variance of the
transverse components of the wave vector. Moreover, we extent our treatment to
the enhancement of beam shifts via weak measurements and relate our results to
recent experiments.
