Question

在此上下文中，对于在整个实例创建中定义为0的参数“amount”有什么区别，因为注释行下面的代码执行相同的操作而没有“amount = 0”？

class Account
    attr_accessor :balance
    def initialize(amount=0)
        self.balance = amount
    end
    def +(x)
        self.balance += x
    end
    def -(x)
        self.balance -= x
    end
    def to_s
        balance.to_s
    end
end

acc = Account.new(20)
acc -= 5
puts acc

class Account
    attr_accessor :balance
    def initialize(amount)
        self.balance = amount
    end
    def +(x)
        self.balance += x
    end
    def -(x)
        self.balance -= x
    end
    def to_s
        balance.to_s
    end
end

acc = Account.new(20)
acc -= 5
puts acc

我是初学者。谢谢你的帮助！

Answer 1

在参数列表中指定amount = 0会使amount参数成为可选参数（默认值为0）。

如果您未指定amount参数，则为0。

account = Account.new  # without amount argument
account.balance # => 0

account = Account.new 10  # with amount argument
account.balance # => 10

Answer 2

唯一的区别是：

第一个类设置默认值


    class Account
        attr_accessor :balance
        def initialize(amount=0)
            self.balance = amount
        end
        ... class omitted

    end

    account = Account.new
    account.balance # should be equal to 0


      class Account
        attr_accessor :balance
        def initialize(amount)
            self.balance = amount
        end
      ... class omitted

      end

      account = Account.new nil
      account.balance # should be equal to nil

参数之间的差异＆＃34;金额＆＃34;和＆＃34;金额= 0＆＃34;，在这种情况下？

2 个答案: