# File lib/dm-core/resource/persistence_state/clean.rb, line 7
        def set(subject, value)
          if not_modified?(subject, value)
            self
          else
            # assign to persistence_state so that if Dirty#set calls
            # a Relationship#set, which modifies a Property, the same
            # Dirty state instance will be reused.
            state = resource.persistence_state = Dirty.new(resource)
            state.set(subject, value)
          end
        end