[ 文章收集 ] alias vs alias_method

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Preface
It comes up very often. Should I use alias or alias_method . Lets take a look at them in a bit detail.

alias vs alias_method
Usage of alias

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1. class User  
2.   
3.   def full_name  
4.     puts "Johnnie Walker"  
5.   end  
6.   
7.   alias name full_name  
8. end  
9.   
10. User.new.name #=>Johnnie Walker  

Usage of alias_method

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1. class User  
2.   
3.   def full_name  
4.     puts "Johnnie Walker"  
5.   end  
6.   
7.   alias_method :name, :full_name  
8. end  
9.   
10. User.new.name #=>Johnnie Walker  

First difference you will notice is that in case of alias_method we need to use a comma between the "new method name" and "old method name". alias_method takes both symbols and strings as input. Following code would also work:

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1. alias_method 'name', 'full_name'  

That was easy. Now lets take a look at how scoping impacts usage of alias and alias_method.

Scoping with alias

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1. class User  
2.   
3.   def full_name  
4.     puts "Johnnie Walker"  
5.   end  
6.   
7.   def self.add_rename  
8.     alias_method :name, :full_name  
9.   end  
10. end  
11.   
12. class Developer < User  
13.   def full_name  
14.     puts "Geeky geek"  
15.   end  
16.   add_rename  
17. end  
18.   
19. Developer.new.name #=> 'Gekky geek'  

In the above case method "name" picks the method "full_name" defined in "Developer" class. Now lets try with alias.

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1. class User  
2.   
3.   def full_name  
4.     puts "Johnnie Walker"  
5.   end  
6.   
7.   def self.add_rename  
8.     alias :name :full_name  
9.   end  
10. end  
11.   
12. class Developer < User  
13.   def full_name  
14.     puts "Geeky geek"  
15.   end  
16.   add_rename  
17. end  
18.   
19. Developer.new.name #=> 'Johnnie Walker'  

With the usage of alias the method "name" is not able to pick the method "full_name" defined in Developer.

This is because alias is a keyword and it is lexically scoped. It means it treats self as the value of self at the time the source code was read. In contrast alias_method treats self as the value determined at the run time. Overall my recommendation would be to use alias_method. Since alias_method is a method defined in class Module it can be overridden later and it offers more flexibility.

Supplement
* Blog - Method alias in ruby

You can create aliases for a method and variable name in ruby. This can be helpful if you want to override the behavior of some method without changing the origin implementation of it. alias_method take a new_name as a copy name of the old_name and it has the following syntax:

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1. alias_method (new_name, old_name)