Patching class methods in Ruby

original.rb

module Document
  extend ActiveSupport::Concern

  module ClassMethods
    def key(name, type)
      puts "a new key `#{name}` in `#{type}` is declared."
    end
  end
end

class User
  include Document

  key :name, Symbol
end

patched.rb

module Document
  extend ActiveSupport::Concern

  module ClassMethods
    def key(name, type)
      puts "a new key `#{name}` in `#{type}` is declared."
    end
  end
end

module Patch
  module PatchedClassMethods
    def key(name, type)
      raise "Symbol type is deprecated" if type == Symbol
      super
    end
  end

  def included(model)
    super
    model.singleton_class.prepend(PatchedClassMethods)
  end
end

Document.singleton_class.prepend(Patch)

class User
  include Document

  key :name, Symbol
end