最低限の before_action っぽいもの

before_action.rb

class Foo
  def self.before_action(hook, only:)
    actions = Array(only)
    self.prepend Module.new {
      actions.each do |action|
        class_eval <<-RUBY, __FILE__, __LINE__+1
          def #{action}
            #{hook}
            super
          end
        RUBY
      end
    }
  end

  before_action :foo, only: :show
  before_action :hook, only: %i[show save]

  def save
    p :save
  end

  def show
    p :show
  end

  def foo
    p :foo
  end

  def hook
    p :hook
  end
end

Foo.new.show # => :hook, :foo, :show
Foo.new.save # => :hook, :save