为什么/如何 ActiveSupport::Concern 改变祖先查找顺序？

Question

考虑以下代码：

require 'active_support/concern'

module Inner
end

module Outer
  extend ActiveSupport::Concern
  included do
    include Inner
  end
end

class FirstClass
  include Outer
end

module SecondInner
end

module SecondOuter
  include SecondInner
end

class SecondClass
  include SecondOuter
end

为什么通过 AS::Concern 包含的模块的祖先顺序与普通的 Ruby 不同？

FirstClass.ancestors
# => [FirstClass, Inner, Outer, Object, PP::ObjectMixin, Kernel, BasicObject]

SecondClass.ancestors
# => [SecondClass, SecondOuter, SecondInner, Object, PP::ObjectMixin, Kernel, BasicObject]

Answer 1

ActiveSupport::Concern 不改变祖先查找顺序。

如果您将 更改module Outer为使用纯 Ruby 来执行相同的操作，那么 AS 在没有 AS 的情况下会做什么，您会看到它具有相同的祖先链：

module Outer
  def self.included(base)
    base.send(:include, Inner)
  end
end

SecondClass.ancestors
#=> [SecondClass, SecondOuter, SecondInner, Object, PP::ObjectMixin, Kernel, BasicObject]