  We investigate the possibility of implementing a given projection measurement
using linear optics and arbitrarily fast feedforward based on the continuous
detection of photons. In particular, we systematically derive the so-called
Dolinar scheme that achieves the minimum error discrimination of binary
coherent states. Moreover, we show that the Dolinar-type approach can also be
applied to projection measurements in the regime of photonic-qubit signals. Our
results demonstrate that for implementing a projection measurement with linear
optics, in principle, unit success probability may be approached even without
the use of expensive entangled auxiliary states, as they are needed in all
known (near-)deterministic linear-optics proposals.
