How to alias a class method within a module?

Question

I am using Ruby v1.9.2 and the Ruby on Rails v3.2.2 gem. I had the following module ``` module MyModule extend ActiveSupport::Concern included do def self.my_method(arg1, arg2) ... end end end ``` and I wanted to alias the class method `my_method`. So, I stated the following (not working) code: ``` module MyModule extend ActiveSupport::Concern included do def self.my_method(arg1, arg2) ... end # Note: the following code doesn't work (it raises "NameError: undefined # local variable or method `new_name' for #<Class:0x00000101412b00>"). def self.alias_class_method(new_name, old_name) class << self alias_method new_name, old_name end end alias_class_method :my_new_method, :my_method end end ``` In other words, I thought to extend the `Module` class someway in order to add an `alias_class_method` method available throughout `MyModule`. However, I would like to make it to work and to be available in all my Ruby on Rails application. - Where I should put the file related to the Ruby core ex…

Accepted Answer

You could use `define_singleton_method` to wrap your old method under a new name, like so:

```
module MyModule
  def alias_class_method(new_name, old_name)
    define_singleton_method(new_name) { old_name }
  end
end

class MyClass
  def my_method
    puts "my method"
  end
end

MyClass.extend(MyModule)
MyClass.alias_class_method(:my_new_method, :my_method)
MyClass.my_new_method     # => "my method"
```

Answering your comment, you wouldn't have to extend every single class by hand. The `define_singleton_method` is implemented in the `Object` class. So you could simply extend the `Object` class, so every class should have the method available...

```
Object.extend(MyModule)
```

Put this in an initializer in your Rails app and you should be good to go...

How to alias a class method within a module?

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