Question

以下代码导致nil，我无法弄清楚原因。我的初始化有问题吗？

class Card
    VALUES = %w(2 3 4 5 6 7 8 9 10 J Q K A)
    SUITS = %w(S H D C)

    def initialize(suit, value)
        @suit = suit
        @value = value
    end
end

class Deck
    attr_accessor :cards

    def initialize
        @cards = []
        Card::SUITS.each do |suit|
            Card::VALUES.each do |value|
                @cards << Card.new(suit, value)
            end
        end
    end
end

Deck.new

p @cards

Answer 1

在对象之外不知道

curl $(docker-machine ip default):49160。在类@cards之外，它是Ruby中顶级作用域的实例变量。

您必须使用访问者方法来获取内容：

Deck

Answer 2

或只是：

my_deck = Deck.new

p my_deck.cards

Answer 3

简而言之，实例变量只能通过同一类中的其他方法来查看。我相信你要做的是：

new_deck = Deck.new
p new_deck.cards

在cards上调用new_deck方法会返回@cards。

Answer 4

您创建了一个新对象Deck.new，但是您不打印其cards的值 - 您打印的@cards实例变量在此上下文中为{{1} }}

你可能想要像nil这样的东西。

Answer 5

目前，@cards数组的输出很难读取并包含对象信息。我以为我会提供另一种选择，我希望它有所帮助：

class Deck

  attr_writer :suits, :values
  attr_accessor :deck

  def initialize
    suits
    values
    generate_deck
    shuffle
  end

  def generate_deck
    @deck = []
    @suits.each do |suit|
      @values.each { |value| @deck << [suit, value] }
    end
  end

  def suits
    @suits  = ['Clubs', 'Diamonds', 'Hearts', 'Spades' ]
  end

  def values
    @values = ('2'..'10').to_a + ['J','Q','K','A']
  end

  #just in case you want to shuffle your deck
  def shuffle
    @deck.shuffle!
  end

end

require 'pp' #this makes the output prettier
new_deck = Deck.new
pp new_deck.deck #calls your current deck so you can see it

输出示例：

$ ruby yourfilename.rb
[["Hearts", "K"],
 ["Spades", "5"],
 ["Clubs", "7"],

 #code omitted... (the rest of your cards would be here)

 ["Clubs", "K"],
 ["Hearts", "5"],
 ["Diamonds", "J"],
 ["Hearts", "7"]]

尝试初始化一副牌时的零级别

5 个答案: