From: transfire@...
Date: 2006-07-10T22:44:32+09:00
Subject: Re: instance_exec

Duh! I'm sitting here screwing with this and the answer's sitting one
directory over.. with only a minor modification (I added recv=nil) I
introduce you to Facets' Proc#to_method:

  #--
  # Credit for #to_method goes to Forian Gross (flgr).
  #--

  require 'thread'

  class Proc

    MethodMutexes = Hash.new do |hash, key|
      hash[key] = Mutex.new
    end

    # Creates a local method based on a Proc.
    def to_method(name=nil, recv=nil)
      name ||= "!to_method_temp#{self.object_id}"
      recv ||= eval("self", self)
      klass = recv.class
      MethodMutexes[klass => name].synchronize do
        begin
          klass.send(:define_method, name, &self)
          return recv.method(name)
        ensure
          klass.send(:remove_method, name) if not name
        end
      end
    end

  end

Then instance_exec is simply:

  module Kernel

    def instance_exec(*args, &block)
      block.to_method(nil,self).call(*args)
    end

  end

Proof is in the pudding. Facets' really does pay off!

T.