类变量和扩展模块

发布于 2024-09-29 20:29:55 字数 777 浏览 3 评论 0原文

我有一个如下所示的模块

module MyModule
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def foo
      @@var = 1
    end

    def bar
      puts @@var
    end
  end
end

class A
  include MyModule
  foo
end

class B < A; end

，但是

 B.bar outputs '1'.

，我希望仅在调用 .foo 时才定义 .bar 。我尝试过，

module MyModule
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def foo
      @@var = 1
      extend SingletonMethods
    end

  module SingletonMethods
    def bar
      puts @@var
    end
  end
end

问题是

B.bar

返回错误“MyModule::SingletonMethods 中未初始化的类变量@@var”。如何才能使 .foo 中定义的变量可用于 .bar？

原文

I have a module like the following

module MyModule
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def foo
      @@var = 1
    end

    def bar
      puts @@var
    end
  end
end

class A
  include MyModule
  foo
end

class B < A; end

so that

 B.bar outputs '1'.

However, I would like to have .bar only be defined if .foo is called. I tried

module MyModule
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def foo
      @@var = 1
      extend SingletonMethods
    end

  module SingletonMethods
    def bar
      puts @@var
    end
  end
end

The problem is that

B.bar

returns the error "uninitialized class variable @@var in MyModule::SingletonMethods". How can I make it so that a variable defined in .foo is available to .bar?

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給妳壹絲溫柔 2024-10-06 20:29:55

使用 mattr_accessor 代替

回复收藏 0 原文

与君绝 2024-10-06 20:29:55

我能够使用 self 语法从模块访问类变量

class User
  include Base
  @@attributes = [:slug, :email, :crypted_password]
end

module Base
  def self.included(base)
  base.extend ClassMethods
end

def headers
  if defined? self.attributes
    self.attributes
  end
 end
end

现在调用 User.headers 给了我预期的结果
[:slug, :email, :crypted_password]

如果有人可以进一步解释为什么这在 ruby 中如此有效，请告诉我！

I was able to access class variables from a module using the self syntax

class User
  include Base
  @@attributes = [:slug, :email, :crypted_password]
end

module Base
  def self.included(base)
  base.extend ClassMethods
end

def headers
  if defined? self.attributes
    self.attributes
  end
 end
end

Now calling User.headers gives me the expected result of
[:slug, :email, :crypted_password]

If anyone can shed more light on why this works exactly so in ruby, please let me know!

回复收藏 0 原文

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