Ruby - 失败语句/保护条件返回 nil

Posted 2023-02-15

【中文标题】Ruby - 失败语句/保护条件返回 nil

【英文标题】：Ruby - Fail statement/Guard Condition returning nil

【发布时间】：2019-05-22 06:18:06

【问题描述】：

我正在尝试改进release_bike 方法。 我已经进入 irb，第一个保护条件有效，并且 release_working_bikes 工作，但第二个保护条件在 irb 中一直返回 nil，即使我运行功能测试并且知道只有一辆损坏的自行车可用。

我对第二条失败线的表述方式是否有问题，或者broken_bikes 中是否存在缺陷？

release_bike 方法应该如下工作； 如果扩展坞中没有自行车，那么应该有一个警告说 - No bikes available 如果扩展坞中有自行车，但它们全部坏了，那么应该有一个警告说 - No working bikes available 如果有一些工作自行车，那么release_bike 应该释放其中一辆工作自行车。

以下是涉及的两个类；

require_relative 'bike'
class DockingStation
  DEFAULT_CAPACITY = 20
  attr_reader :capacity, :bikes

  def initialize(capacity = DEFAULT_CAPACITY)
    @bikes = []
    @capacity = capacity

  end

  def release_bike
    fail 'No bikes available' if empty?
    fail 'No working bikes available' unless broken_bikes
    release_working_bikes

  end

  def dock(bike)
    fail 'Docking Station Full' if full?
    @bikes << bike
  end

  private

  def working_bikes
    @bikes.each  |bike| return bike unless bike.broken? 
  end

  def broken_bikes
    not_working = []
    not_working << @bikes.each  |bike| return bike if bike.broken? 
    not_working.empty?
  end

  def release_working_bikes
    bike = working_bikes
    @bikes.delete(bike)
  end

  def full?
    @bikes.count >= @capacity
  end

  def empty?
    @bikes.empty?
  end

end



class Bike
  attr_accessor :broken

  def initialize
    @broken = false
  end

  def working?
    @working
  end

  def report_broken
    @broken = true
  end

  def broken?
    @broken
  end

end

【问题讨论】：

您似乎没有检查 所有 自行车是否损坏，请尝试制作一种方法来检查并在防护条件下使用它

@bikes.each |bike| return bike if bike.broken? 如果自行车坏了，这将从方法中返回bike，如果没有一辆自行车坏了，它将把自行车的完整列表推到 not_working 数组中。

我想你要找的是@bikes.all?(&:broken?)，它将检查是否所有的自行车都坏了

@engineersmnky 谢谢，这正是我正在寻找的。我是Ruby的新手，是：坏了吗？被称为符号，因为它是一种方法？

【参考方案1】：

正如 cmets 中已经指出的那样，您正在尝试检查是否所有自行车都坏了，所以为什么不将您的方法命名为 all_bikes_broken? 。见代码中的 cmets。

require_relative 'bike'
class DockingStation
  DEFAULT_CAPACITY = 20
  attr_reader :capacity, :bikes

  def initialize(capacity = DEFAULT_CAPACITY)
    @bikes = []
    @capacity = capacity

  end

  def release_bike
    fail 'No bikes available' if empty?
    fail 'No working bikes available' unless all_bikes_broken?
    release_working_bikes

  end

  def dock(bike)
    fail 'Docking Station Full' if full?
    @bikes << bike
  end

  private

  def working_bikes
    #this will select only bikes which are NOT broken
    @bikes.reject |bike| bike.broken? 
  end

  def all_bikes_broken?
    #this is shorthand for @bikes.all? |bike| bike.broken? 
    #it says send  :broken? method to each instance of bike.
    #.all? returns true only if all instances return true, otherwise false.
    @bikes.all?(&:broken?)
  end

  def release_working_bikes
    bike = working_bikes
    @bikes.delete(working_bikes.first)
    #or you could do .last but order probably doesn't matter here.
  end

  def full?
    @bikes.count >= @capacity
  end

  def empty?
    @bikes.empty?
  end

end


class Bike
  attr_accessor :broken

  def initialize
    @broken = false
  end

  def working?
    @working
  end

  def report_broken
    @broken = true
  end

  def broken?
    @broken
  end

end

【讨论】：

release_working_bikes 将成为一个问题，因为working_bikes 是一个集合。 select ! 通常也是 reject

@engineersmnky 很好地抓住了release_working_bikes，修复了这个问题，当然.reject 更好，谢谢。