类实例变量是类私有的。继承的类不能直接访问它们。这里有几种方法。
1.定义访问器
module MyModule
def self.included(base)
base.instance_variable_set :@my_instance_variable, {}
base.extend ClassMethods
end
module ClassMethods
def my_instance_variable
# self is ClassA here, so we need to call superclass
superclass.instance_variable_get :@my_instance_variable # => {}
end
end
end
class MySuperClass
include MyModule
end
class ClassA < MySuperClass; end
ClassA.my_instance_variable # => {}
2. 更多元程序化
但是每次从你那里继承一个类时都会调用一个钩子。此时您可以设置变量。看一下这个。
module MyModule
def self.included(base)
base.extend ClassMethods
end
module ClassMethods
# make it a class method. It will be called on target classes later.
def enhance klass
klass.instance_variable_set("@my_instance_variable", {})
end
end
end
class MySuperClass
include MyModule
# this hook will get called on 'class ClassA < MySuperClass`
def self.inherited klass
# set class instance var on child class
enhance klass
end
end
class ClassA < MySuperClass; end
ClassA.instance_variable_get '@my_instance_variable' # => {}
注意:在这个示例中,每个继承的类都有自己的类实例 var(而基类没有)。这可能更适合您的情况,可能不是。