refactor_handling_bad_input_example.rb

    class Table

      def initialize(data = [], options = {})
        check_type data
        data.each do |row| 
          check_type row
          check_length row, data.first.length
        end
        
        @header_support = options[:headers]
        set_headers(data.shift) if @header_support
        
        @rows = data
      end

      def add_row(new_row, pos=nil)
        check_type new_row
        check_length new_row, @rows.first.length
        
        i = pos.nil? ? @rows.length : pos
        @rows.insert(i, new_row)
      end
   
   
      def add_column(col, pos=nil)
        check_type col
        check_length col, @rows.length
        
        i = pos.nil? ? @rows.first.length : pos
        
        if @header_support
          headers.insert(i, col.shift)
        end
        
        @rows.each do |row|
          row.insert(i, col.shift)
        end
      end

    private

      def check_type(data)
        raise ArgumentError, "Input is not an array" \
          unless Array === data
      end
      
      def check_length(data, expected)
        raise ArgumentError, "Input length is inconsistent" \
          unless data.length == expected
      end

    end