Ruby：NoMethodError：变异实例变量时未定义的方法答案

【问题标题】：Ruby: NoMethodError: undefined method when Mutating Instance VariableRuby：NoMethodError：变异实例变量时未定义的方法
【发布时间】：2024-08-10 21:50:02
【问题描述】：

我正在编写一个程序来重新安排公交车上的乘客。我想记录重新排序公共汽车座位需要多少次洗牌。以为我拥有它，但我无法更改self.reshuffle_count。如何通过reshuffle_seating方法访问@reshufffle_count

class MagicBus < Array

  attr_writer :seating

  def seating
    @seating || []
  end

  def reshuffle_count
    @reshuffle_count || 0
  end

def reshuffle_seating
    max_passengers = self.seating.max
    popular_seat = self.seating.max
    pop_seat_indx = self.seating.find_index(popular_seat)
    reshuffle_num = 0
    self.seating.rotate!(pop_seat_indx)
    while popular_seat > 1 do 
      self.seating.each_with_index do |seat, index|
      if index != 0
        self.seating[index] = self.seating[index] +1
        popular_seat = popular_seat -1
      else
        reshuffle_num = reshuffle_num +1
        p reshuffle_num
      end
      end
    end
    self.seating.rotate!(pop_seat_indx*-1)
    self.seating[pop_seat_indx] = popular_seat
    self.reshuffle_count = reshuffle_num   
  end
end

class TestMagicBusSeating < MiniTest::Test
def test_reshuffle_seating_instance1
    bus = MagicBus.new
    bus.seating = [0,2,7,0]
    bus.reshuffle_seating
    assert_equal([2, 4, 1, 2], bus.seating)
    assert_equal(5, bus.reshuffle_count)
  end
end

错误信息是

Error:
TestMagicBusSeating#test_reshuffle_seating_instance1:
NoMethodError: undefined method `reshuffle_count=' for []:MagicBus
Did you mean?  reshuffle_count
    magic_bus.rb:99:in `reshuffle_seating'
    magic_bus.rb:217:in `test_reshuffle_seating_instance1'

【问题讨论】：

这里从数组继承是一件不寻常的事情。目的是什么？看起来你甚至没有使用那个角度。
您的意思可能是@reshuffle_count = ...，因为您没有attr_writer。

标签： ruby methods instance

【解决方案1】：

NoMethodError：未定义的方法`reshuffle_count='

这意味着您缺少setter。您定义了 getter def reshuffle_count 但没有 setter。

class MagicBus < Array

  attr_writer :seating

  def seating
    @seating || []
  end

  def reshuffle_count=(value)
    @reshuffle_count=value
  end

  def reshuffle_count
    @reshuffle_count || 0
  end
  .....

或者正如@tadman 指出的那样，attr_writer :resuffle_count

【讨论】：

这会生成.... Error: TestMagicBusSeating#test_reshuffle_seating_instance1: NoMethodError: undefined method reshuffle_count' for []:MagicBus 你是说什么？ reshuffle_count=magic_bus.rb:219:in test_reshuffle_seating_instance1'
用班级更新了答案。
我不需要def reshuffle_count=(value) @reshuffle_count=value end 否则解决了错误

【解决方案2】：

除了接受的答案外，您还可以直接访问同一类的其他方法中的实例变量。

class MagicBus < Array

  def reshuffle_count
    @reshuffle_count || 0
  end

  def reshuffle_seating
    ...
    @reshuffle_count = reshuffle_num
  end 
end

请注意，如果您定义， attr_writer :resuffle_count 那么MagicBus 实例也可以在类外读/写变量。

magic_bus = MagicBus.new
magic_bus.resuffle_count # valid

除非您将 attr_writer :resuffle_count 放在私有范围内。

class MagicBus < Array
  ...
  def reshuffle_seating
    ... 
    reshuffle_count = reshuffle_num   
  end

  private

  attr_writer :resuffle_count
end

现在resuffle_count只能在类内部访问。

【讨论】：