prependでモジュールを拡張する例

prepend_example.rb

module Bar
  def bar
    "bar"
  end
end

class Foo
  include Bar
end

foo1 = Foo.new
puts foo1.bar

module Baz
  def bar_with_patch
    "#{bar_without_patch} with patch"
  end

  def self.prepended(mod)
    mod.module_eval do
      alias_method :bar_without_patch, :bar
      alias_method :bar, :bar_with_patch
    end
  end
end

Bar.prepend(Baz)

puts foo1.bar
foo2 = Foo.new
puts foo2.bar