application.rb

config.to_prepare do
  Dir.entries("app/extensions")
    .select{ |f| !File.directory? f}
    .each do |file_name|

    array = file_name.split("_")
    array.pop
    klass_name = array.map(&:capitalize).join
    klass = klass_name.constantize

    klass.class_eval do
      include "#{klass}Extensions".constantize
    end
  end
end