试图理解在 Ruby 中使用 self.method_name 与 Classname.method_name [英] Trying to understand use of self.method_name vs. Classname.method_name in Ruby

问题描述

我试图了解何时使用 self.method_name 与何时使用 Classname.method_name.

I'm trying to understand when to use self.method_name vs. when to use Classname.method_name.

在下面的示例中，为什么before_create"需要引用User.hash_password"而不是self.hash_password"或仅引用hash_password"?

In the example below, why does "before_create" need to reference "User.hash_password" instead of "self.hash_password" or just "hash_password"?

因为我们已经在 User 类中，我认为 before_create 方法会知道"hash_password"是它自己类的成员，不需要任何特殊的语法来引用它.

Since we are in the User class already, I thought the before_create method would "know" that "hash_password" is a member of its own class and would not need any special syntax to refer to it.

require 'digest/sha1'

class User < ActiveRecord::Base

  attr_accessor :password
  attr_accessible :name, :password

  validates_presence_of :name, :password
  validates_uniqueness_of :name

  def before_create
    self.hashed_password = User.hash_password(self.password)
  end

  def after_create
    @password = nil
  end

  def self.login(name, password)
    hashed_password = hash_password(password || "")
    self.find(:first, :conditions => ["name = ? and hashed_password = ?", name, hashed_password])
  end

  def try_to_login
    User.login(self.name, self.password)
  end

  private

  def self.hash_password(password)
    Digest::SHA1.hexdigest(password)
  end

end

推荐答案

def before_create
   self.hashed_password = User.hash_password(self.password)
end

在这个例子中，User.hash_password 调用了 class User 上的 hash_password 方法，而 >self.hashed_pa​​ssword= 在 User 的这个特定实例上调用 hashed_pa​​ssword= 方法.

In this example, User.hash_password calls the hash_password method on the class User, whereas self.hashed_password= calls the hashed_password= method on this particular instance of User.

如果你用 self.hash_password 替换 User.hash_password，Ruby 会抱怨 NoMethodError，因为没有实例方法的名称hash_password 存在于 User 类中.不过，您可以将其替换为 self.class.hash_password.

If you replace User.hash_password with self.hash_password, Ruby would complain with a NoMethodError, because no instance method by the name of hash_password exists in the class User. You could replace it with self.class.hash_password, though.

如果将 self.hashed_pa​​ssword= 替换为简单的 hashed_pa​​ssword=，Ruby 将创建一个名为 hashed_pa​​ssword 的局部变量，而不是调用实例方法 hashed_pa​​ssword=.如果要调用属性编写器，则需要显式添加 self.

If you replace self.hashed_password= with simply hashed_password=, Ruby would create a local variable named hashed_password, rather than call the instance method hashed_password=. You need to explicitly add self if you want to call attribute writers.

方法定义中的self (def self.hash_password) 使hash_password 成为类方法而不是实例方法.在这种情况下，self 指的是 class.在实例方法的上下文中，self 指的是一个实例.

The self in the method definition (def self.hash_password) makes hash_password a class method instead of an instance method. In this context, self refers to the class. In the context of an instance method, self refers to an instance.

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