define_hook_method.rb

# ref:
# http://blog.kymmt.com/entry/hook-by-alias-chaining-in-ruby
# http://miyohide.hatenablog.com/entry/2014/02/28/203743

module AddLogging
  def self.included(base)
    base.extend HookMethod
  end

  module HookMethod
    def hook_class_method(*methods)
      methods.each do |method|
        orig = "#{method}_without_logging".to_sym

        singleton_class.send(:alias_method, orig, method)

        define_singleton_method(method) do |*args, &block|
          result = send(orig, *args, &block)
          puts 'hook message'
          result
        end
      end
    end

    def hook_instance_method(*methods)
      methods.each do |method|
        orig = "#{method}_without_logging".to_sym

        alias_method orig, method

        define_method(method) do |*args, &block|
          result = send(orig, *args, &block)
          puts 'hook message'
          result
        end
      end
    end
  end
end

class Hello
  include AddLogging
  def say_hello(str)
    puts "hello, #{str}"
  end

  def foobar
    puts "foobar"
  end

  class << self
    def bar
      puts "bar"
    end
  end
end

# define hook methods.
hello = Hello.new
Hello.hook_instance_method(:say_hello, :foobar)
Hello.hook_class_method(:bar)

# run methods.
hello.say_hello("world")
hello.foobar
Hello.bar