RegisterBinaryCallbackHandler typedef

ZoneBinaryCallback<R, T1, T2> RegisterBinaryCallbackHandler <R, T1, T2>(Zone self, ZoneDelegate parent, Zone zone, R f(T1 arg1, T2 arg2))

Implementation 

typedef RegisterBinaryCallbackHandler
    = ZoneBinaryCallback<R, T1, T2> Function<R, T1, T2>(Zone self,
        ZoneDelegate parent, Zone zone, R Function(T1 arg1, T2 arg2) f);