From: Robert Klemme <bob.news@...>
Date: 2005-09-20T01:06:37+09:00
Subject: Re: help with tricky proc/binding issue

Pit Capitain wrote:
> Ara.T.Howard schrieb:
>> 
>> i'm trying to be able to define a proc that can be called in the
>> context of self, eg:
>> 
>>   block = lambda{ p 42 }
>>   an_obj.instance_eval &block
>> 
>> but which can also be called with arguments, for example (imaginary
>> ruby): 
>> 
>>   b = lambda{|x| p [x, y]}
>> 
>>   class C
>>     def y; 42; end
>>   end
>> 
>>   c = C::new
>>   x = 42
>> 
>>   c.arg_instance_eval(x, &b)  #=> [42, 42]
>> 
>> any ideas?
> 
> Tom (aka Trans) recently mentioned that he changed procs into methods
> in order to get what you want. Here's a quick hack, not efficient and
> not thread-safe, but maybe a start:
> 
>    class Object
>      def arg_instance_eval( *args, &block )
>        c = class << self; self; end
>        c.send( :define_method, :arg_instance_eval_method, &block )
>        arg_instance_eval_method( *args )
>      ensure
>        c.send( :remove_method, :arg_instance_eval_method )
>      end
>    end

Hacky but nice!  For thread safety how about:

   class Object
     def arg_instance_eval( *args, &block )
       c = class << self; self; end
       meth = "__m_#{Thread.current.object_id}_#{rand 666}"
       c.send( :define_method, meth, &block )
       send( meth, *args )
     ensure
       c.send( :remove_method, meth )
     end
   end

Kind regards

    robert