Override this method to specify how this
PTransform
should be expanded on the given
InputT
.
NOTE: This method should not be called directly. Instead apply the
PTransform
should
be applied to the
InputT
using the
apply
method.
Composite transforms, which are defined in terms of other transforms, should return the
output of one of the composed transforms. Non-composite transforms, which do not apply any
transforms internally, should return a new unbound output and register evaluators (via
backend-specific registration methods).