From: Simon Chiang <simon.a.chiang@...>
Date: 2010-05-02T04:20:29+09:00
Subject: class in instance_eval -- what the namespace?

I'm confused as to how the parent constant is determined when you
define a class within an instance_eval.  It appears that sometimes
ruby decides to use a nameless, perhaps temporary class as the parent
constant.

Interestingly enough, the behavior is different when you use a block
vs a string, and ruby implementation to implementation.  For example
consider this script:

  [script.rb]
  obj = Object.new

  obj.instance_eval do
    class A; end
    puts A
  end
  puts A rescue puts $!.message

  obj.instance_eval %q{
    class B; end
    puts B
  }
  puts B rescue puts $!.message

Running this across several implementations produces a variety of
results:

  % rvm ruby script.rb
  jruby-1.4.0: jruby 1.4.0 (ruby 1.8.7 patchlevel 174) (2009-11-02
69fbfa3) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_17) [x86_64-java]
  A
  A
  #<Class:01x3a98350a>::B
  uninitialized constant B
  rbx-1.0.0-rc4: rubinius 1.0.0-rc4 (1.8.7 release 2010-03-31 JI)
[x86_64-apple-darwin10.3.0]
  A
  A
  B
  B
  ruby-1.8.7-p249: ruby 1.8.7 (2010-01-10 patchlevel 249) [i686-
darwin10.2.0]
  A
  A
  #<Class:0x10019c3b8>::B
  uninitialized constant B
  ruby-1.9.1-p378: ruby 1.9.1p378 (2010-01-10 revision 26273) [i386-
darwin10.2.0]
  #<Class:0x000001008481e0>::A
  uninitialized constant A
  #<Class:0x000001008481e0>::B
  uninitialized constant B

Any thoughts?  And specifically, does anyone know of a way to set the
default namespace for the class keyword?  Specifying the full constant
name like 'class ::A' works to assign the constants and uniformly
produce a rubinius-like output but I was wondering if there is another
way.