From: "Florian Groß" <flgr@...>
Date: 2003-06-05T06:42:06+09:00
Subject: Re: case of sub! not working

This is a multi-part message in MIME format.
--------------040007020705010202080704
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit

Ian Macdonald wrote:
> Hi,

Moin!

> irb(main):002:0> ENV['PATH'].sub!(%r(:/usr/kerberos/bin), '')
> => "/usr/bin:/bin:/usr/X11R6/bin:/usr/pubsw/bin"
> irb(main):003:0> ENV['PATH']
> => "/usr/bin:/bin:/usr/X11R6/bin:/usr/pubsw/bin:/usr/kerberos/bin"
>
> Why doesn't the sub! work in line 002? It returns the correct answer,
> but ENV['PATH'] is not modified in-place. 

You now know why this isn't the case, but I chose to try making it 
work anyway. I attached a small hack which changes the original ENV[] 
and ENV[]= so that they return a proxy to the real contents which 
changes ENV[] when it is changed.

This allows you to do this:

ENV['foo'] = "hello world"	# => "hello world"
ENV['foo'].replace("whatever").reverse!.gsub!(/[aeiou]/, "*")
				# => "r*v*t*hw"
ENV['foo']			# => "r*v*t*hw"

I didn't really test this in detail so it might have small bugs or 
break your Ruby into tiny little shivers.

Regards,
flgr

--------------040007020705010202080704
Content-Type: text/plain;
 name="proxied_env.rb"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="proxied_env.rb"

class << ENV
  class EnvEntryProxy
    def initialize(entry_name)
      @entry_name = entry_name
    end

    def method_missing(method_name, *args)
      entry = ENV.old_get(@entry_name)
      result = entry.send(method_name, *args)
      ENV.old_set(@entry_name, entry)
      result = EnvEntryProxy.new(@entry_name) if result.id == entry.id
      return result
    end

    ["to_s","to_a","inspect","==","=~","==="].each { |method_name|
      class_eval <<-END
        def #{method_name}(*args)
          method_missing('#{method_name}', *args)
        end
      END
    }
  end

  alias :old_get :[]
  def [](entry_name)
    EnvEntryProxy.new(entry_name)
  end

  alias :old_set :[]=
  def []=(entry_name, new_value)
    old_set(entry_name, new_value)
    EnvEntryProxy.new(entry_name)
  end
end
--------------040007020705010202080704--