```ruby
# encoding: utf-8
require 'ruby-dmm/response/item'

module DMM
  class Response
    attr_reader :request, :result

    def initialize(response)
      @request = response[:request][:parameters][:parameter].inject({}) {|hash, params| hash.merge(params[:name].to_sym => params[:value]) }
      if response[:result][:message] && response[:result][:errors]
        @result  = response[:result]
      else
        @result  = DMM::Response::Result.new(response[:result])
      end
    end

    class Result
      RESULT_KEYS = [
        :first_position,
        :items,
        :result_count,
        :total_count,
      ]
      attr_reader *RESULT_KEYS

      def initialize(result)
        RESULT_KEYS.each do |key|
          case key
          when :items
            @items = [result[:items][:item]].flatten.map do |item|
              DMM::Response::Item.new(item)
            end if result.key?(:items)
            @items ||= []
          else
            instance_variable_set("@#{key}", result[key].to_i)
          end
        end
      end
    end
  end
end
```

Add alias method for `DMM::Result` class
user
```ruby
# encoding: utf-8
require 'ruby-dmm/response/item'

module DMM
  class Response
    attr_reader :request, :result

    def initialize(response)
      @request = response[:request][:parameters][:parameter].inject({}) {|hash, params| hash.merge(params[:name].to_sym => params[:value]) }
      if response[:result][:message] && response[:result][:errors]
        @result  = response[:result]
      else
        @result  = DMM::Response::Result.new(response[:result])
      end
    end

    class Result
      RESULT_KEYS = [
        :first_position,
        :items,
        :result_count,
        :total_count,
      ]
      attr_reader *RESULT_KEYS
      alias_method :offset,     :first_position
      alias_method :per_result, :result_count

      def initialize(result)
        RESULT_KEYS.each do |key|
          case key
          when :items
            @items = [result[:items][:item]].flatten.map do |item|
              DMM::Response::Item.new(item)
            end if result.key?(:items)
            @items ||= []
          else
            instance_variable_set("@#{key}", result[key].to_i)
          end
        end
      end
    end
  end
end
```
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