如何使用“自我"? Rails中的关键字 [英] How to use the "self" keyword in Rails

问题描述

关于Rails中的关键字self，我知道该关键字引用了类本身的一个实例.例如，在self.encrypted_password中.

Regarding the keyword self in Rails, I know that the keyword refers to an instance of the class itself. For example, in self.encrypted_password.

我几乎不知道为什么在右侧作为参数传递的属性password也没有以self关键字作为前缀吗?

I have less of an idea why the attribute password, passed as an parameter on the right hand side, isn't prefixed with the self keyword too?

class User < ActiveRecord::Base

  attr_accessor :password
  attr_accessible  :name, :email, :password, :password_confirmation

  validates :password, :presence     => true,
                      :confirmation => true,
                      :length       => { :within => 6..40 }

  before_save :encrypt_password

  private

  def encrypt_password
    self.encrypted_password = encrypt(password)
  end

  def encrypt(string)
    string # Only a temporary implementation!
  end
end

有人可以解释何时使用或不使用self关键字吗?

Can someone explain when to use, or not use, the self keyword?

推荐答案

答案

答案很简单:范围可见性.

Answer

The answer is simple: scope visibility.

def encrypt_password
  self.encrypted_password = encrypt(password)
end

有(或者应该在运行时应该有)称为password的东西.在您的情况下，它是数据库中的一个属性.但它也可以是局部变量.如果找不到该名称，则会引发错误.

There is (or, rather, there should be at runtime) something called password. In your case, it's an attribute from the database. But it also can be a local variable. If such name isn't found, error will be raised.

但是您必须在encrypted_password之前加上self前缀，以明确声明您将要更新实例属性.否则，将创建新的局部变量encrypted_password.显然，这不是您想要的效果.

But you have to prefix encrypted_password with self to explicitly state that you're going to update instance attribute. Otherwise, new local variable encrypted_password will be created. Obviously, not the effect you wanted.

这是一小段代码

class Foo
  attr_accessor :var

  def bar1
    var = 4
    puts var
    puts self.var
  end
end

f = Foo.new
f.var = 3
f.bar1

输出

4
3

因此，如我们所见，var被分配为没有self关键字，因此，在作用域中现在有两个名称var:局部变量和实例属性.实例属性被局部变量隐藏，因此，如果您确实要访问它，请使用self.

So, as we can see, var is assigned without self keyword and, because of this, now there are two names var in the scope: local variable and instance attribute. Instance attribute is hidden by local variable, so if you really want to access it, use self.

这篇关于如何使用“自我"? Rails中的关键字的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！