AbstractWhether or not we're still processing rows.
Defaults to true (processing rows), but is set to false once
rounds has been visited.
Visits a row. If we're still visiting (i.e. rounds hasn't been reached) then we pass that row to derived classes for processing.
Optionalblock: AbstractBlockProtected AbstractvisitUnderlying visitor implementation (to be overridden by derived classes).
Optionalblock: AbstractBlock
Base class for all visitors
Defers to derived classes in order to process rows, but does check whether rounds has been reached and stops processing at that point.