From: Robert Dober <robert.dober@...>
Date: 2010-10-21T03:53:17+09:00
Subject: Re: [Q] best practice for redefining methods at runtime?

On Wed, Oct 20, 2010 at 5:31 PM, Chuck Remes <cremes.devlist@mac.com> wrote:

> Is that reasonable or is there a more idiomatic way of accomplishing this task?
Reasonable maybe but it is far from achieving what freeze does,
because you still have instance_variable_set and as long as this
available I can redefine the accesors, thus you would need to block
#instance_variable_set, #define_method for the class but I can still
beat that for any given instance by introducing singleton methods....
In other words it is a metaprogramming mess.sub("m","h").gsub("s","l")!

Maybe you should reconsider your approach, what about freezing the
object but accessing it in a wrapper that rescues the exceptions? This
could done via closures, and BasicObject makes the task much easier
than it was in 1.8

class Freezer < BasicObject
  freezee = nil
  define_method :initialize do | f |
    freezee = f
  end
  define_method :method_missing do | name, *args, &blk |
    begin
      freezee.send( name, *args, &blk )
    rescue ::RuntimeError => re
     # Pitty that there is no designated Exception for this BTW
      raise unless /can't modify frozen/ === re.message
    end
  end
end

a = Freezer.new( "" )
a << "1"
puts a
a.freeze
a << "2"
puts a
# But
a.xxx

HTH
R.

-- 
There are worse things than having people misunderstand your work. A
worse danger is that you will yourself misunderstand your work.
-- Paul Graham