红宝石中的模块和类变量作用域 [英] Module and class variable scope in ruby

问题描述

我仍在尝试清楚地了解Module/Class/Instance变量...

I am still trying to clearly understand Module/Class/Instance variables ...

我的代码当前看起来像这样...

My code currently looks something like this ...

module Foo
  @@var1 ={}
  @@var2 =[]
  @@var3 = nil

  def m1(value)
    @@var2 << value
  end

  def m2(value)
    @@var1[@@var3]=value
  end
end

class Bar
  include Foo
  p @@var1
end

class Bar2
  include Foo
  p @var1
end

我正在尝试创建一个模块，该模块包含针对每个类的行为的类范围配置.配置存储在@@ var1和@@ var2中.使用此代码，变量可在包括该模块的所有类之间共享.这不是期望的结果，我希望每个类都具有自己的行为配置.

I am trying to create a module that contains a class-wide configuration for how each class will behave. The configuration is stored in @@var1 and @@var2. Using this code the variables are shared across ALL classes that include the module. This is not the desire result, I want each class to have it's own behavior configuration.

我还尝试创建一个包含模块的单个类，并创建变量，但是模块无法访问这些变量.

I have also tried creating a single class that includes the module and also creates the variables but then the variables are not accessible by the module.

module Foo

  def m1(value)
    @@var2 << value
  end

  def m2(value)
    @@var1[@@var3]=value
  end
end

class T
  @@var1 ={}
  @@var2 =[]
  @@var3 = nil

  include foo
end

class Bar < T
  p @@var1
end

class Bar2 < T
  p @var1
end

我还读到，拥有带有类变量的模块不是很好的编码风格，但是我想不出一种方法来实现此功能……

I have also read that having modules with class variables is not good coding style but I cannot think of a way to achieve my functionality with this ...

在此先感谢您的帮助

推荐答案

首先-类变量是邪恶的，应避免使用(因为它们也被所有子类继承，并且通常带来的弊大于利.

Firstly - class variables are evil and should be avoided (because they are also inherited by all subclasses and usually causes more harm than good.

您要在包含给定模块的类或模块上创建类实例变量(而非类变量).使用included方法很容易:

You want to create a class instance variable (not class variable) on a class or module which is including given module. It is easy to do with included method:

module Foo
  @default_settings = {}

  module ClassMethods
    def foo_settings
      @foo_settings
    end
  end

  def self.included(target)
    target.instance_variable_set('@foo_settings', @default_settings.dup)
    target.extend ClassMethods
  end    
end

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