def method_missing(sym, *ignore)
    key = sym.to_s
    index = @keys.index(key)
    if index
      @values.at(index)
    else
      raise RuntimeError.new("unknown field: " + key)
    end
  end
def method_missing(sym, *ignore)
    key = sym.to_s
    index = @keys.index(key)
    if index
      @values.at(index)
    else
      raise RuntimeError.new("unknown field: " + key)
    end
  end
can accept 2 arguments: keys array, values array
 or 1 argument: a hash