Rubyにおけるフックメソッドとメソッド呼び出しへのフックの追加例

class String
  def self.inherited(subclass)
    puts "#{self} was inherited by #{subclass}"
  end
end
class MyString < String; end

String was inherited by MyString

module AfterCall
 def self.included(base)
  base.extend(ClassMethods)
 end
 module ClassMethods
  def after_call when_call,then_call,*args_then,&block_then
   alias_method "old_#{when_call}",when_call
   define_method when_call do |*args_when,&block_when|
    send "old_#{when_call}",*args_when,&block_when
    send then_call,*args_then,&block_then
   end
  end
 end
end
class Student
 include AfterCall
 def enter_class sb
  puts "enter class #{sb}"
  yield('before') if block_given?
 end
 private
 def after_enter_class pop
  puts "after enter class #{pop}"
  yield('after') if block_given?
 end
 protected
 def third_after
  puts "from third enter"
 end

 after_call :after_enter_class ,:third_after
 after_call :enter_class ,:after_enter_class,"doubi", &lambda {|x|puts "from lambda #{x}"}
end
Student.new.enter_class "1" do |x|
 puts "from lambda #{x}"
end

#enter class 1
#from lambda before
#after enter class doubi
#from lambda after
#from third enter