From: ts <decoux@...>
Date: 2008-03-22T22:20:57+09:00
Subject: Re: ruby19 and defined?

Rick DeNatale wrote:
 > Hmmmm, not so sure that that's actually a bug.

  It's a bug

  Here the bytecode

vgs% ./ruby -ve 'puts 
VM::InstructionSequence.compile("defined?(a.b)").disasm'
ruby 1.9.0 (2008-03-21 revision 15825) [i686-linux]
<compiled>:1: warning: useless use of defined? in void context
== disasm: <ISeq:<compiled>@<compiled>>=================================
0000 putself                                                          (   1)
0001 defined          21, :a, false
0005 leave
0006 pop
0007 branchif         12
0009 putnil
0010 leave
0011 pop
0012 putnil
0013 send             :a, 0, nil, 24, <ic>
0019 defined          13, :b, true
0023 leave
vgs%

  Now if I add 'p'

vgs% ./ruby -ve 'puts VM::InstructionSequence.compile("p 
defined?(a.b)").disasm'
ruby 1.9.0 (2008-03-21 revision 15825) [i686-linux]
== disasm: <ISeq:<compiled>@<compiled>>=================================
0000 putnil                                                           (   1)
0001 putself
0002 defined          21, :a, false
0006 jump             24
0008 branchif         13
0010 putnil
0011 jump             24
0013 putnil
0014 send             :a, 0, nil, 24, <ic>
0020 defined          13, :b, true
0024 send             :p, 1, nil, 8, <ic>
0030 leave
vgs%



  See the bytecode 'jump 24' in 0006


Guy Decoux