Question

我创建了以下课程

class BankAccount                                                       
  def accountNumber                                                   
    @accountNumber=5                                                
  end                                                                 
  def accountNumber=(value)                                           
    @accountNumber=value                                            
  end                                                                 
end

我这样使用它：

account=BankAccount.new
=> #<BankAccount:0x0000000295d6c8>
account.accountNumber
=> 5
account.accountNumber="223"
=> 223
account.accountNumber
=> 5

为什么即使将accountNumber设置为5也等于223？

Answer 1

调用account.accountNumber时，它会调用accountNumber 方法，您将其定义为：

def accountNumber                                                   
  @accountNumber=5                                                
end

有几种解决方法，一个简单的方法是：

class BankAccount
  attr_accessor :account_number

  def initialize(account_number=5)
    @account_number = account_number
  end
end

哪个作品很棒：

irb(main):009:0> x = BankAccount.new
=> #<BankAccount:0x00007fae449c5fc8 @account_number=5>
irb(main):010:0> x.account_number = 10
=> 10
irb(main):011:0> y = BankAccount.new
=> #<BankAccount:0x00007fae4495fed0 @account_number=5>
irb(main):012:0> y.account_number
=> 5
irb(main):013:0> z = BankAccount.new
=> #<BankAccount:0x00007fae480066a0 @account_number=5>
irb(main):015:0> z.account_number = 15
=> 15
irb(main):016:0> z.account_number
=> 15

Here是SO attr_accessor工作原理的答案。

Answer 2

由于您的方法，每次致电account.accountNumber时，您都将@accountNumber分配为5。

要避免这种情况，您可以这样做：

class BankAccount
  DEFAULT_NUMBER = 5
  DEFAULT_AMOUNT = 10

  attr_accessor :number, :amount

  def initialize
    set_default_values
  end

  def set_default_values
    @number = DEFAULT_NUMBER
    @amount = DEFAULT_AMOUNT
  end
end

现在您可以根据需要分配值

account = BankAccount.new # => #<BankAccount:0x000055d581adbd38 @number=5 @amount=10>

account.number = 500
account.number # => 500

account.amount = 20
account.amount # => 20

account.amount = BankAccount::DEFAULT_AMOUNT
account.amount # => 10

account.set_default_values
account # => #<BankAccount:0x000055d581adbd38 @number=5 @amount=10>

实例变量的持久值

2 个答案: