prependの説明

prepend.rb

module M
  class hoge
    puts 'hoge'
  end
end

class C
  prepend M
end

a = C.new
a.hoge #=> hoge

prepend_ancestors.rb

module M
  class hoge
    puts 'hoge'
  end
end

class C
  prepend M
end

C.ancestors #=>[M, C, Object, PP::ObjectMixin, Kernel, BasicObject]