From: eric.promislow@...
Date: 2005-07-30T10:36:04+09:00
Subject: Better way to extend Kernel#eval -- can't require 'openssl'

This program doesn't work
(ruby 1.8.2 (2004-12-25) [i386-mswin32]):

# ==== 8-< =====
module Kernel
  alias_method :old_eval, :eval
  def eval(*args)
    res = old_eval(*args)
    print "**** eval(#{args}) => #{res}\n"
    return res
  end
end

require 'openssl'

print "Done\n"
# ==== 8-< =====

If I run it I get this output:

eval_wrapper.rb:4:in `eval': (eval):1:in `eval': uninitialized constant
Kernel::
Cipher (NameError)
        from c:/ruby/lib/ruby/site_ruby/1.8/openssl/cipher.rb:24:in
`old_eval'
        from eval_wrapper.rb:4:in `eval'
        from c:/ruby/lib/ruby/site_ruby/1.8/openssl/cipher.rb:24
        from c:/ruby/lib/ruby/site_ruby/1.8/openssl/cipher.rb:23:in
`each'
        from c:/ruby/lib/ruby/site_ruby/1.8/openssl/cipher.rb:23
        from c:/ruby/lib/ruby/site_ruby/1.8/openssl.rb:20:in `require'
        from c:/ruby/lib/ruby/site_ruby/1.8/openssl.rb:20
        from eval_wrapper.rb:10:in `require'
        from eval_wrapper.rb:10

Here's the problematic code from openssl:

module OpenSSL
  module Cipher
    %w(AES Cast5 BF DES Idea RC2 RC4 RC5).each{|cipher|
      eval(<<-EOD)
        class #{cipher} < OpenSSL::Cipher::Cipher
          def initialize(*args)
            args = args.join('-')
            if args.size == 0
              super(\"#{cipher}\")
            else
              super(\"#{cipher}-#\{args\}\")
            end
          end
        end
      EOD
    }

If I change the first line in the eval block from "... < Cipher"
to "< OpenSSL::Cipher::Cipher" it works.

The problem is obviously that the hook causes the eval block to be
eval'ed in the hook's binding, not the original binding.  What's
the best way to get the binding I need?  Yes, I have a trace-function,
but I don't see an obvious event that tells me the eval hook is
about to be called.

Thanks,
Eric