From: Robert Feldt <robert.feldt@...>
Date: 2006-03-31T16:57:35+09:00
Subject: Redef undef'ed methods?

How "final" is a call to undef_method? Is there any way to get the
method back, ie. hook it up to the class again?

From my understanding of the C code it seems impossible since the
function/method pointer is set to 0 and there is no way from Ruby to
access the original value for that pointer again (unless you have
extracted "it" earlier with one of the "*method" methods). Is this
analysis correct?

If so code like

module Kernel
  [:eval, :system, :exec, :callcc, :`,               # `
   :set_trace_func, :sleep, :syscall].each do |m|
    undef_method m
  end
end

class Module
  [:module_eval, :class_eval,
   :define_method, :method, :instance_method,
   :private_class_method].each do |m|
    undef_method m
  end
end

class Object
  [:instance_eval].each {|m| undef_method m}
end

etc would give a possibility for a kind of simple, fine-grained
"sandboxing"? (I'm not implying you should do this instead of
tainting/SAFE-levels etc, just exploring possibilities)

Thanks,

Robert Feldt