From: Robert Feldt <feldt@...>
Date: 2001-06-18T06:56:05+09:00
Subject: [ruby-talk:16579] Re: Trapping method defs

On Sat, 16 Jun 2001, Mathieu Bouchard wrote:

> > ? RCR? Or one can easily get it from 'caller' as in my previously
> > proposed call_stack RCR...
> 
> Not sure how you'd do that... I don't think "def" will appear in the
> call stack. I expect something weird to happen, like a half-blank
> entry or a missing entry or two half-missing entries (e.g. Ruby code
> appears to be calling method_added itself...) but that's pure speculation.
> 
Ok. Matz?

> > I sure hope this is already supported in some way I've missed...
> 
> I have played a bit with #method_added a few weeks ago...
> 
> def Integer.method_added(sym)
> 	if sym==:%
> 		puts "I find your lack of faith... disturbing"
> 		Process.kill 11, Process.pid
> 	end
> end
> 
> but then, Hurst and I figured out that:
> 
> a. #method_added can be redefined or removed without your #method_added
> being actually called.
> 
> b. unless you freeze Module ;-)
> 
> c. doesn't prevent anyone from def'ing a singleton #method_added without
> you getting to know anything about it. 
> 
Can't I use Object.singleton_method_added?

> d. you still don't have info about the replaced method...
> 
> sorry, haven't pushed this further.
> 
Maybe if you continue on something like:

class Object
  def Object.method_added(methodId)
    puts "ORG: Added method #{self.inspect}##{methodId.id2name}"
  end
  @@defining_method_added = false
  def Object.singleton_method_added(methodId)
    if methodId == :method_added
      if @@defining_method_added
	@@defining_method_added = false
      else
	puts "Added singleton method #{self.inspect}.#{methodId.id2name}"
	@@defining_method_added = true
	# Reinstall our method_added!
	self.instance_eval <<-'EOC'
	  alias new_method_added method_added
	  def method_added(methodId)
	    new_method_added(methodId)
	    puts "REI: Added method #{self.inspect}##{methodId.id2name}"
          end
        EOC
      end
     else
       unless self == Object and methodId == :singleton_method_added
	 puts "Added singleton method #{self.inspect}.#{methodId.id2name}"
       end
     end
  end
end

class C
  def im1
  end
  def C.method_added(methodId)
    puts "C: Added method #{self.inspect}##{methodId.id2name}"
  end
  def im2
  end
end

but you'll have to reinstall the singleton_method_added in
singleton_method_added if someone tries to redef
Object.singleton_method_added. And then they can probably use undef_method
and/or remove_method anyway and on it goes...

Maybe there is not a fully "safe" way but my alternative is to
use a trace func and then it wont work if someone sets another trace
func... (and I can't afford the typical factor 50 slowdown of using
trace funcs).

Anyway thanks for your input!

/Robert