From: Logan Capaldo <logancapaldo@...>
Date: 2006-07-15T02:02:42+09:00
Subject: Re: Preferred monkeypatching technique


On Jul 14, 2006, at 8:25 AM, Daniel Martin wrote:

> Tom Werner <tom@helmetstohardhats.org> writes:
>
>> class Firetruck
>>    alias_method :__old_put_out_fire, :put_out_fire
>>    def put_out_fire(options = {})
>>       __old_put_out_fire(options.merge({:nozzle => :big}))
>>    end
>> end
>
> It seems to me that you're asking for a ruby version of gensym.  (See
> any lisp reference that talks about lisp macro writing) So let's try
> to make something like that:
>
> # In the framework core
>
> class Firetruck
>   def put_out_fire(options = {})
>     puts "Extinguishing with options #{options.inspect}"
>   end
> end
>
> # In plugin1
>
> class Symbol
>   def Symbol.gensym
>     @@gensym_count ||= 0
>     @@gensym_count += 1
>     ("__gensym__%X" % @@gensym_count).intern
>   end
> end
>
> class Firetruck
>   oldmethsym = Symbol.gensym
>   alias_method oldmethsym, :put_out_fire
>   class_eval %Q[
>     def put_out_fire(options = {})
>       #{oldmethsym}(options.merge({:nozzle => :big}))
>     end
>   ]
> end
>
>
> ## Now, in plugin 2
>
> # Note that the same exact code is included for gensym, but
> # that this isn't a problem
> class Symbol
>   def Symbol.gensym
>     @@gensym_count ||= 0
>     @@gensym_count += 1
>     ("__gensym__%X" % @@gensym_count).intern
>   end
> end
>
>

Neat idea, gensym in Ruby. I would suggest making it thread-safe though:

% cat gensym.rb
require 'mutex'
class Symbol
   GensymLock = Mutex.new
   def self.gensym
     GensymLock.synchronize {
       @@gensym_count ||= 0
       @@gensym_count += 1
       ("__gensym__%X" % @@gensym_count).intern
     }
   end
end

And just require it whenever you need it.

require 'gensym'
sym = Symbol.gensym
alias_method sym, :blah