Rails 模块中的 mattr_accessor 是什么? [英] What is mattr_accessor in a Rails module?

问题描述

我在 Rails 文档中真的找不到这个，但似乎 'mattr_accessor' 是 'attr_accessor' 的 Module 推论(getter & setter)在一个普通的Ruby 类中.

I couldn't really find this in Rails documentation but it seems like 'mattr_accessor' is the Module corollary for 'attr_accessor' (getter & setter) in a normal Ruby class.

例如.在一个班级

class User
  attr_accessor :name

  def set_fullname
    @name = "#{self.first_name} #{self.last_name}"
  end
end

例如.在一个模块中

module Authentication
  mattr_accessor :current_user

  def login
    @current_user = session[:user_id] || nil
  end
end

此辅助方法由 ActiveSupport 提供.

This helper method is provided by ActiveSupport.

推荐答案

Rails 通过 mattr_accessor(模块访问器)和 cattr_accessor(以及 _reader/_writer 版本).由于Ruby的attr_accessor为实例生成getter/setter方法，cattr/mattr_accessor在类提供getter/setter方法或模块级.因此:

Rails extends Ruby with both mattr_accessor (Module accessor) and cattr_accessor (as well as _reader/_writer versions). As Ruby's attr_accessor generates getter/setter methods for instances, cattr/mattr_accessor provide getter/setter methods at the class or module level. Thus:

module Config
  mattr_accessor :hostname
  mattr_accessor :admin_email
end

是:

module Config
  def self.hostname
    @hostname
  end
  def self.hostname=(hostname)
    @hostname = hostname
  end
  def self.admin_email
    @admin_email
  end
  def self.admin_email=(admin_email)
    @admin_email = admin_email
  end
end

两个版本都允许您像这样访问模块级变量:

Both versions allow you to access the module-level variables like so:

>> Config.hostname = "example.com"
>> Config.admin_email = "[e-mail]"
>> Config.hostname # => "example.com"
>> Config.admin_email # => "[e-mail]"

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