From: Rick DeNatale <rick.denatale@...>
Date: 2010-02-04T12:01:16+09:00
Subject: Re: hooking subscript operations in a hash

On Wed, Feb 3, 2010 at 9:38 PM, Ralph Shnelvar <ralphs@dos32.com> wrote:
> In order to help debug something, I'd like to hook the hash subscript operation.
>
> I've tried this (and several variants) in irb ... but it doesn't do what I want it to.
>
>
> module RalphMod
>  def []=(index, value)
>    p index
>    p value
>    if index == 'PATH_INFO' and value == '/undefined'
>      puts 'found it!'
>    end
>    super index, value
>  end
> end
>
> class Hash
>  extend RalphMod
> end
>
> env = {}
> env['X'] = 'Y'
> env['PATH_INFO'] = '/undefined'
>
>
> The values are not displayed and 'found it!' is also not displayed.

A few problems with this code.

First

   class Hash
       extend RalphMod
    end

   makes the method in RalphMod a method of the Hash class object not
hash instances.

The way to do that would be

  class Hash
     include RalphMod
  end

but this wouldn't work either because methods in included modules come
after methods defined in the class, so you'll still invoke the
original []= method.

What you want is something like this:

module RalphMod
 def []=(index, value)
   p index
   p value
   if index == 'PATH_INFO' and value == '/undefined'
     puts 'found it!'
   end
   super index, value
 end
end
env = {}
env.extend RalphMod
env['X'] = 'Y'
env['PATH_INFO'] = '/undefined'

This effectively inserts your module between the instance of Hash
referenced by the variable env and it's class.





-- 
Rick DeNatale

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