我应该在Ruby中为类静态变量使用类变量还是类实例变量?

问题描述

class Something
    @@variable = 'Class variable'

    def give_me
        @@variable
    end
end

class OtherThing
    @variable = 'Instance variable with an interface'

    class << self
        attr_accessor :variable
    end

    def give_me
        self.class.variable
    end
end

p Something.new.give_me
p OtherThing.new.give_me

我想知道的是，我应该使用哪一个?每种都有哪些优点和缺点?

What I want to know is, which one should I use?Which are the benefits and cons of each?

类变量是:

1. 除非您进行界面设置，否则为私人
2. 在继承之间共享
3. 写短片

类实例变量为:

1. 公开，因为您必须使用界面才能访问它们
2. 在继承之间不共享，但在继承时设置为nil
3. 渴望写作

我还有什么想念的?

推荐答案

我最近发现ActiveSupport定义了 class_inheritable_accessor ，它具有class-instance变量的优点，即对象不会跨继承共享，并且在子类化时可以为变量设置默认值.

I recently discovered ActiveSupport defines class_inheritable_accessor, which does what the class-instance variables do with the advantage that objects are not shared across inheritance, and you can have a default value for the variable when subclassing.

class Foo
  class_inheritable_accessor :x, :y
end

Foo.x = 1

class Bar < Foo
end

Bar.x #=> 1
Bar.x = 3
Bar.x #=> 3
Foo.x #=> 1

更多信息此处

仅出于完整性考虑:在提出的两个选项中，我更喜欢使用class-instance变量，因为这通常是预期的行为.

Just for completeness: of the two presented options, I prefer going with the class-instance variables, since is often the expected behavior.

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