def in(set)
      @collection = @collection.collect do |item|
        item if set.include?(item.send(@field_name.to_sym))
      end.compact
    end
def in(set)
      @collection = @collection.collect do |item|
        item if set.include?(item.send(@field_name.to_sym))
      end.compact
    end
def in ( set ) @collection = @collection . collect do | item | item if set . include? ( item . send ( @field_name . to_sym ) ) end . compact end
performs a set-inclusion test.

 Task.find(:id).in([3, 5, 9])
performs a set - inclusion test .