alias_method_chain方法在3.1以后的替代使用方式

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

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再看一个
Ruby代码

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

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就说这个事现在流行的方式怎么调：
Ruby代码

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

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super是上一个module里同名方法
include有个顺序覆盖
Ruby代码

1.   module PreExtension; end  
   
2.   module PostExtension; end  
   
3.   
   
4.   include PreExtension   
   
5.   include PostExtension   
   
6. end  
   
7.   
   
8. Something.ancestors # => [Something, Something::PostExtension, Something::PreExtension, Object, Kernel]  
   
9. 
   
10. 
    
11.   module PreExtension; end
    
12.   module PostExtension; end
    
13. 
    
14.   include PreExtension
    
15.   include PostExtension
    
16. end
    
17. 
    
18. Something.ancestors # => [Something, Something::PostExtension, Something::PreExtension, Object, Kernel]

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Ruby代码

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

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