def filter(o)
      raise ArgumentError.new('Wrong type supplied to filter') unless Splib.type_of?(o, @type)
      do_filter(o)
    end
def filter(o)
      raise ArgumentError.new('Wrong type supplied to filter') unless Splib.type_of?(o, @type)
      do_filter(o)
    end
t:: type of Objects filter is to be applied to
 Create a new Filter
 o:: Object from Pipeline
 Applies filter to Object