Rubyでメソッドの定義場所を確認する
gem pry を使うと、$で簡単に確認できる
$ "".present? # From: /home/kinosuke/app/vendor/bundle/ruby/2.3.0/gems/activesupport-4.2.7/lib/active_support/core_ext/object/blank.rb @ line 23: # Owner: Object # Visibility: public # Number of lines: 3 # # def present? # !blank? # end