When I was making some tests of Class::HPLOO, where multiple documents are filtered in the same process, I found a very strange bug, that only happens if you use my and recursivity in a strange way.

Soo, I tried to isolate the bug and make sample of it:

{ package RecMy ;

  use strict ;

sub rec {
  my $n = shift ;
  return if !$n ;
  
  rec( --$n ) ;

  my $local = "[$n] set" if ($n/3) !~ /\./ ;
 
  $local .= ' append' ;
  
  print "<$n> $local\n" ;

}

  for(1..5) {
    print "--------------------- $_\n" ;
    rec(4);  
  }
}
[download]

The BUGGED output is:

--------------------- 1
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 2
<0> [0] set append
<1>  append append
<2>  append append
<3> [3] set append
--------------------- 3
<0> [0] set append
<1>  append append append
<2>  append append append
<3> [3] set append
--------------------- 4
<0> [0] set append
<1>  append append append append
<2>  append append append append
<3> [3] set append
--------------------- 5
<0> [0] set append
<1>  append append append append append
<2>  append append append append append
<3> [3] set append
[download]

But the right output should be:

--------------------- 1
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 2
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 3
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 4
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 5
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
[download]

And to produce the right output I have just changed one line of the code:

  ## changed from (bugged):
  my $local = "[$n] set" if ($n/3) !~ /\./ ;

  ## to (fine):
  my $local ;
  $local = "[$n] set" if ($n/3) !~ /\./ ;
[download]

Soo, why this happens? It seems that my() creates the same scalar 2 times? Or the scalar is not destroied after end the scope of the sub? Or this is a optimization bug? I think that this is a reference count bug, but I haven't looked the Perl CORE yet to really say that.

Note that the bug only happens if the interpolation exists, that is made by:

... if ($n/3) !~ /\./ ;
[download]

I saw the bug first on Perl-5.6.1, than I saw it on Perl-5.8.2 and Perl-5.8.3 too. Soo, wasn't patched yet!

I will wait some advices from the monks before send it to perlbug...