alias_method_chain方法在3.1以后的替代使用方式

三里屯摇滚

alias_method_chain方法在3.1以后的替代使用方式

alias_method_chain()
是rails里的一个广泛使用的方法，简单说，就是你要重写一个方法，在里面加上一个新方法后，还要使用同名的原方法调用。

使用和实现如下，


Ruby代码

1. 1.class Klass   
   
2. 2.  def salute_with_log   
   
3. 3.    puts "Calling method..."  
   
4. 4.    salute_without_log   
   
5. 5.    puts "...Method called"  
   
6. 6.  end  
   
7. 7.  
   
8. 8.  alias_method :salute_without_log, :salute  
   
9. 9.  alias_method :salute, :salute_with_log  
   
10. 10.end  
    
11. 11.  
    
12. 12.Klass.new.salute   
    
13. 13.# Prints the following:   
    
14. 14.# Calling method...   
    
15. 15.# Aloha!   
    
16. 16.# ...Method called  
    
17. class Klass
    
18.   def salute_with_log
    
19.     puts "Calling method..."
    
20.     salute_without_log
    
21.     puts "...Method called"
    
22.   end
    
23. 
    
24.   alias_method :salute_without_log, :salute
    
25.   alias_method :salute, :salute_with_log
    
26. end
    
27. 
    
28. Klass.new.salute
    
29. # Prints the following:
    
30. # Calling method...
    
31. # Aloha!
    
32. # ...Method called

复制代码

再看一个

Ruby代码

1. 1.module InstanceMethods   
   
2. 2.  def deliver_with_switchable_smtp!(mail = @mail)   
   
3. 3.    unless logger.nil?   
   
4. 4.      logger.info  "Switching SMTP server to: #{custom_smtp.inspect}"   
   
5. 5.    end  
   
6. 6.    ActionMailer::Base.smtp_settings = custom_smtp unless custom_smtp.nil?   
   
7. 7.    deliver_without_switchable_smtp!(mail = @mail)   
   
8. 8.  end  
   
9. 9.end  
   
10. 10.def self.included(receiver)   
    
11. 11.  receiver.send :include, InstanceMethods   
    
12. 12.  receiver.class_eval do  
    
13. 13.    alias_method_chain :deliver!, :switchable_smtp  
    
14. 14.  end  
    
15. 15.end  
    
16. 16.d  
    
17.   module InstanceMethods
    
18.     def deliver_with_switchable_smtp!(mail = @mail)
    
19.       unless logger.nil?
    
20.         logger.info  "Switching SMTP server to: #{custom_smtp.inspect}"
    
21.       end
    
22.       ActionMailer::Base.smtp_settings = custom_smtp unless custom_smtp.nil?
    
23.       deliver_without_switchable_smtp!(mail = @mail)
    
24.     end
    
25.   end
    
26.   def self.included(receiver)
    
27.     receiver.send :include, InstanceMethods
    
28.     receiver.class_eval do
    
29.       alias_method_chain :deliver!, :switchable_smtp
    
30.     end
    
31.   end
    
32. end

复制代码

就说这个事现在流行的方式怎么调：

Ruby代码

1. 1.class Something   
   
2. 2.  module Base     
   
3. 3.    def my_method   
   
4. 4.      # (A) original functionality   
   
5. 5.    end  
   
6. 6.  end  
   
7. 7.  
   
8. 8.  module PreExtension   
   
9. 9.    def my_method   
   
10. 10.      # (B) before the original   
    
11. 11.      super # calls whatever was my_method before this definition was made   
    
12. 12.    end  
    
13. 13.  end  
    
14. 14.  
    
15. 15.  module PostExtension   
    
16. 16.    def my_method   
    
17. 17.      super # calls whatever was my_method before this definition was made   
    
18. 18.      # (C) after the original   
    
19. 19.    end  
    
20. 20.  end  
    
21. 21.  
    
22. 22.  include Base # this is needed to place the base methods in the inheritance stack   
    
23. 23.  include PreExtension # this will override the original my_method   
    
24. 24.  include PostExtension # this will override my_method defined in PreExtension   
    
25. 25.end  
    
26. 26.  
    
27. 27.s = Something.new  
    
28. 28.s.my_method   
    
29. 29.#=> this is a twice extended method call that will execute code in this order:   
    
30. 30.#=> (B) before the original   
    
31. 31.#=> (A) the original   
    
32. 32.#=> (C) after the original  
    
33. class Something
    
34.   module Base  
    
35.     def my_method
    
36.       # (A) original functionality
    
37.     end
    
38.   end
    
39. 
    
40.   module PreExtension
    
41.     def my_method
    
42.       # (B) before the original
    
43.       super # calls whatever was my_method before this definition was made
    
44.     end
    
45.   end
    
46. 
    
47.   module PostExtension
    
48.     def my_method
    
49.       super # calls whatever was my_method before this definition was made
    
50.       # (C) after the original
    
51.     end
    
52.   end
    
53. 
    
54.   include Base # this is needed to place the base methods in the inheritance stack
    
55.   include PreExtension # this will override the original my_method
    
56.   include PostExtension # this will override my_method defined in PreExtension
    
57. end
    
58. 
    
59. s = Something.new
    
60. s.my_method
    
61. #=> this is a twice extended method call that will execute code in this order:
    
62. #=> (B) before the original
    
63. #=> (A) the original
    
64. #=> (C) after the original

复制代码

super是上一个module里同名方法
include有个顺序覆盖

Ruby代码

1. 1.  
   
2. 2.  module PreExtension; end  
   
3. 3.  module PostExtension; end  
   
4. 4.  
   
5. 5.  include PreExtension   
   
6. 6.  include PostExtension   
   
7. 7.end  
   
8. 8.  
   
9. 9.Something.ancestors # => [Something, Something::PostExtension, Something::PreExtension, Object, Kernel]  
   
10. 
    
11.   module PreExtension; end
    
12.   module PostExtension; end
    
13. 
    
14.   include PreExtension
    
15.   include PostExtension
    
16. end

复制代码

Something.ancestors # => [Something, Something:ostExtension, Something:reExtension, Object, Kernel]




Ruby代码

1. 1.class SomethingNew   
   
2. 2.  module Base   
   
3. 3.    def my_method   
   
4. 4.      puts "(A)"  
   
5. 5.    end  
   
6. 6.  end  
   
7. 7.  
   
8. 8.  module Extension   
   
9. 9.    def my_method   
   
10. 10.      puts "(B)"  
    
11. 11.      super  
    
12. 12.    end  
    
13. 13.  end  
    
14. 14.  
    
15. 15.  include Base   
    
16. 16.  include Extension   
    
17. 17.end  
    
18. 18.  
    
19. 19.SomethingNew.new.my_method   
    
20. 20.# Output:   
    
21. 21.# >> (B)   
    
22. 22.# >> (A)   
    
23. 23.  
    
24. 24.SomethingNew.ancestors # => [SomethingNew, SomethingNew::Extension, SomethingNew::Base, Object, Kernel]  

复制代码

清风鸟儿

谢谢分享

2gua

屯哥的这不错。