參數「數量」和「數量= 0」之間的區別？

Question

由於在註釋行下面的代碼與out「amount = 0」做同樣的事情，參數「amount」被定義爲0的區別是什麼？

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 

我是個初學者。謝謝你的幫助！

Answer 1

在參數列表中指定amount = 0使參數amount成爲可選參數（其中0作爲其默認值）。

如果您未指定amount參數，則它將爲0。

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

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

Answer 2

唯一的區別是：

第一類設置的默認值

 

    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