Question

从codeschool的ruby-bits课程，我试图了解这些类是如何工作的 - 我有一个Game类和一个名为Library的集合类，它存储了一系列游戏。

class Game
  attr_accessor :name, :year, :system
  attr_reader :created_at

  def initialize(name, options={})
    self.name = name
    self.year = options[:year]
    self.system = options[:system]
    @created_at = Time.now
  end


  def ==(game)
    name == game.name && 
    system == game.system &&
    year == game.year
  end
end

图书馆班：

class Library
  attr_accessor :games

  def initialize(*games)
    self.games = games
  end

  def has_game?(*games)
    for game in self.games
      return true if game == game
    end
    false
  end
end

现在我创造了一些游戏：

contra = Game.new('Contra', {
  year: 1994,
  system: 'nintendo'
})

mario = Game.new('Mario', {
  year: 1996,
  system: 'SNES'
})

sonic = Game.new('Sonic', {
  year: 1993,
  system: 'SEGA'
})

并实例化一个新集合：

myCollection = Library.new(mario, sonic)

当我尝试使用myCollection方法查找某个游戏是否在has_game?时，我总是得到true

puts myCollection.has_game?(contra) #=> returns **true**即使从未作为集合的一部分插入。

我做错了什么？

Answer 1

return true if game == game

我认为这种说法可能会引起问题。

总是如此。

你可能想要这样的东西：

def has_game?(wanted)
  for game in self.games
    return true if game == wanted
  end
  false
end

Answer 2

这里有一些错误：

您应该使用self.XXXX来创建实例变量使用@XXXX，它直接访问值，使用self实际执行另一个方法调用，请参阅此处了解更多详细信息：Instance variable: self vs @
正如提到的其他人game == game将始终返回true，答案就是答案已发布但不允许将多个游戏传递到has_game?

以下是我的更改正常工作：

class Game
  attr_accessor :name, :year, :system
  attr_reader :created_at

  def initialize(name, options={})
    @name       = name
    @year       = options[:year]
    @system     = options[:system]
    @created_at = Time.now
  end


  def ==(game)
    @name == game.name && 
    @system == game.system &&
    @year == game.year
  end
end

class Library
  attr_accessor :games

  def initialize(*games)
    @games = games
  end

  # only returns true if this Library
  # has ALL of the games passed to has_game? 
  def has_game?(*_games)
    _games.each do |game|
      return false if not @games.include?(game)
    end

    return true
  end
end

contra = Game.new('Contra', {
  year: 1994,
  system: 'nintendo'
})

mario = Game.new('Mario', {
  year: 1996,
  system: 'SNES'
})

sonic = Game.new('Sonic', {
  year: 1993,
  system: 'SEGA'
})

myCollection = Library.new(mario, sonic)
puts "Collection has Contra? #{myCollection.has_game?(contra)}"
puts "Collection has Sonic and Mario #{myCollection.has_game?(sonic, mario)}"

输出：

Collection has Contra? false
Collection has Sonic and Mario true

为什么我的ruby方法总是返回true？

2 个答案: