def get(key)
      if @items.include?(key)
        @list.each_index do |i|
          if @list[i] == key
            @list.delete_at(i)
            break
          end
        end
        @list.push(key)
        @items[key]
      else
        return nil unless block_given?
         self[key] = yield
      end
    end
def get(key)
      if @items.include?(key)
        @list.each_index do |i|
          if @list[i] == key
            @list.delete_at(i)
            break
          end
        end
        @list.push(key)
        @items[key]
      else
        return nil unless block_given?
         self[key] = yield
      end
    end
Retrieve item from cache
 Store item returned by given block if any