类变量上的 Attr_accessor [英] Attr_accessor on class variables

问题描述

attr_accessor 不适用于以下代码.错误说undefined method 'things' for Parent:Class (NoMethodError)":

attr_accessor does not work on the following code. The error says "undefined method 'things' for Parent:Class (NoMethodError)":

class Parent
  @@things = []
  attr_accessor :things
end
Parent.things << :car

p Parent.things

但是下面的代码有效

class Parent
  @@things = []
  def self.things
    @@things
  end
  def things
    @@things
  end
end
Parent.things << :car

p Parent.things

推荐答案

attr_accessor 定义实例的访问器方法.如果你想要类级自动生成的访问器，你可以在元类上使用它

attr_accessor defines accessor methods for an instance. If you want class level auto-generated accessors you could use it on the metaclass

class Parent
  @things = []

  class << self
    attr_accessor :things
  end
end

Parent.things #=> []
Parent.things << :car
Parent.things #=> [:car]

但请注意，这会创建一个类级别的实例变量不是一个类变量.无论如何，这可能是您想要的，因为类变量的行为与您在处理继承时可能期望的不同.请参阅Ruby 中的类和实例变量".

but note that this creates a class level instance variable not a class variable. This is likely what you want anyway, as class variables behave differently then you might expect when dealing w/ inheritence. See "Class and Instance Variables In Ruby".

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