From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-11-20T04:54:05+09:00
Subject: Re: Re-opening an existing module and changing a method

On Thu, Nov 19, 2009 at 7:45 PM, Aldric Giacomoni <aldric@trevoke.net> wrote:
> Jesús Gabriel y Galán wrote:
>
>> irb(main):003:1> class << self
>> irb(main):004:2> alias :old_sqrt :sqrt
>> irb(main):005:2> end
>
> Ah-ha! My version is underneath. So, what the bit of code I quoted does
> is.. It reopens "the class of the module" to make a change in the alias?

Yes, module_function creates a method in the singleton class of the module.
So you need to enter that singleton class via class << self to be in a
place where self is that singleton class, in order to be able to alias
that method correctly.


>
> module Math
>
>  class << self
>    alias :old_sqrt :sqrt
>  end
>
>  def self.sqrt x
>    result = old_sqrt(x)
>    if result.is_a? Float
>      "sqrt(#{x})"
>    else
>      result
>    end
>  end
> end
>
>
>>> puts Math.sqrt(2)
> => sqrt(2)

Jesus.