自己在本地实现 rails api 中的实例，但是报错，api 中的实例如下所示：

module HairColors
  mattr_accessor :hair_colors
end

class Person
  include HairColors
end

Person.hair_colors = [:brown, :black, :blonde, :red]
Person.hair_colors     # => [:brown, :black, :blonde, :red]
Person.new.hair_colors # => [:brown, :black, :blonde, :red]

自己本地进行实现：

require 'active_support'

module HairColors
  mattr_accessor :hair_colors
end

class Person
  include HairColors
end

Person.hair_colors = [:brown, :black, :blonde, :red]  #报错 undefined method `hair_colors=' for Person:Class (NoMethodError)
Person.hair_colors     # => [:brown, :black, :blonde, :red]
Person.new.hair_colors # => [:brown, :black, :blonde, :red]

自己的实现与 api 中的实现结果不符，为何？