Question

当我尝试使用我定义的类方法查找实例时，我不确定为什么会收到错误。

bank_account.rb

class BankAccount 
    attr_reader :balance

    def self.create_for(first_name, last_name)
        @accounts ||= []
        @accounts << BankAccount.new(first_name, last_name) 
    end

    def self.find_for(first_name, last_name)
        @accounts.find{|account| account.full_name == "#{first_name} #{last_name}"}
    end

    def initialize(first_name, last_name)
        @balance = 0
        @first_name = first_name
        @last_name = last_name
    end

    def full_name 
        "#{first_name} #{@last_name}"
    end

    def deposit(amount)
        @balance += amount 
    end

    def withdraw(amount)
        @balance -= amount 
    end

end

在irb中，我使用create_for类方法创建了两个银行帐户。

$BankAccount.create_for("Brad", "Pitt")
$BankAccount.create_for("Angelina", "Jolie")

当我试图找到实例时，

$BankAccount.find_for("Angelina", "Joile")

我收到了这个错误：

NameError: undefined local variable or method `first_name' for #<BankAccount:0x007fb914a47700>

我不确定为什么它说没有定义'first_name'。

Answer 1

以下部分

def full_name 
   "#{first_name} #{@last_name}" # <~~ here you missed @ symbol before first_name
end

需要

def full_name 
   "#{@first_name} #{@last_name}"
end

完整代码：

class BankAccount 
    attr_reader :balance

    def self.create_for(first_name, last_name)
        @accounts ||= []
        @accounts << BankAccount.new(first_name, last_name) 
    end

    def self.find_for(first_name, last_name)
        @accounts.find{|account| account.full_name == "#{first_name} #{last_name}"}
    end

    def initialize(first_name, last_name)
        @balance = 0
        @first_name = first_name
        @last_name = last_name
    end

    def full_name 
        "#{@first_name} #{@last_name}"
    end

    def deposit(amount)
        @balance += amount 
    end

    def withdraw(amount)
        @balance -= amount 
    end
    def self.account_holders;@accounts;end

end
BankAccount.create_for("Brad", "Pitt")
BankAccount.create_for("Angelina", "Jolie")
BankAccount.find_for("Angelina", "Jolie")
# => #<BankAccount:0x99de7d0
#     @balance=0,
#     @first_name="Angelina",
#     @last_name="Jolie">

BankAccount.account_holders
# => [#<BankAccount:0x99de8d4
#      @balance=0,
#      @first_name="Brad",
#      @last_name="Pitt">,
#     #<BankAccount:0x99de7d0
#      @balance=0,
#      @first_name="Angelina",
#      @last_name="Jolie">]

创建类方法

1 个答案: