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module の include と extend

Last updated at Posted at 2022-02-22

はじめに

移植やってます。
( from python 3.7 to ruby 2.7 )

wrap (Python)

前回の記事(moduleclass間)でホッとしたのですが、modulemodule間ですと、NoMethodErrorになります。

失敗 (Ruby)

module M
  def my_decorator(meth)
    orig = method(meth)
    define_singleton_method(meth) do |*args, **kwargs|
      puts "Calling decorated method"
      orig.call(*args, **kwargs)
    end
  end  
end

module A
  include M
  module_function

  def _example
    puts "Called decorated method"
  end
  def example
    my_decorator(:_example)
    _example    
  end
end

a = A
a.example

# output
undefined method `define_method'

ぐぬぬ。

成功 (Ruby)

module M
  def my_decorator(meth)
    orig = method(meth)
    define_singleton_method(meth) do |*args, **kwargs|
      puts "Calling decorated method"
      orig.call(*args, **kwargs)
    end
  end  
end

module A
-  include M
+  extend M
  module_function

  def _example
    puts "Called decorated method"
  end
  def example
    my_decorator(:_example)
    _example    
  end
end

a = A
a.example

# output
Calling decorated method
Called decorated method

Module#include は、クラス(のインスタンス)に機能を追加しますが、extend は、ある特定のオブジェクトだけにモジュールの機能を追加したいときに使用します。

ふむふむ、Moduleはインスタンスが生成されないのでincludeでは追加されないと理解。

メモ

  • Ruby の extend を学習した
  • 百里を行く者は九十里を半ばとす
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