Question

我无法理解为什么我的代码不起作用。

class Container
  module Actions 
    @instance_variable = 0;
    def action1
      return @instance_variable # no error, but doesn't return 0! What can be done ?
    end
  end
  include Actions
end

Container.new.action1()

我觉得有一个简单的答案。

Answer 1

您应该将它放在初始化函数中：

class Container
  module Actions 
    def initialize
      @instance_variable = 0;
    end
    def action1
      return @instance_variable # no error, but doesn't return 0! What can be done ?
    end
  end
  include Actions
end

puts Container.new.action1().inspect  ## 0

另一种不太合适的方法是在未设置实例的情况下给出默认值：

class Container
  module Actions 
    def action1
      @instance_variable ||= 0
      return @instance_variable # no error, but doesn't return 0! What can be done ?
    end
  end
  include Actions
end

Answer 2

您的代码无效，因为@instance_variable是Container::Actions模块对象的实例。通过instance_variables检查：

Container::Actions.instance_variables
# => [:@instance_variable]

它与你在课堂上定义的相同（不在initialize中）：

class A
  @var = 42
end
A.instance_variables
# => [:@var]

因此，如果您真的想使用Container::Actions的实例变量，可以使用instance_variable_get：

class Container
  module Actions
    @instance_variable = 0;
      return Actions.instance_variable_get :@instance_variable
     end
   end
   include Actions
 end


 Container.new.action1()

初始化模块实例变量

2 个答案: