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Postings from March 2003
$ perl -le 'sub a { my $p; /(?{ print ++$p })/ } a, a, a'
1
2
3
That should print '1' each time.
This seems to be a very old bug ( see the subject line ).
It happens because the (?{ .. }) block uses another pad than the block
it's in: so '$p' will have a refcount of 2 because it's used in two
different pads ( see S_pad_findlex() in pad.c - :752 ).
When the 'a' returns for the first time, the $p lexical will be
'abandonned' instead of 'cleared' - because its recount is >= 1.
( see scope.c:875 - & run the above script with -DXv ).
So the (?{ CODE }) will stick to the first instance of $p.
The PAD_SAVE_LOCAL, PAD_RESTORE_LOCAL macros at the EVAL: case
in S_regmatch() aren't at all useful: they don't free the lexicals
in the pad, they only switch pads.
The obvious solution is to let (?{ .. }) blocks use the pad of the
block they're in; that will also have the advantage of removing that
pad juggling and make things a little bit faster.
This doesn't mean of course that
{ my $p=1; /(?{ my $p = 2 })/; print $p }
will work differently.
(?{ .. }) blocks will still be properly scoped.
The patch draft below passes all tests and works equally well
with precompiled && run-time compiled regexp's.
Any issues I missed ?
Note:
I think the PAD_SAVE_* macros should be removed completely: they're
flawed and anybody trying to use them will eventually fall in the
same trap.
Regards
Adi
--------------------------------------------------------------------
--- /arc/perl-current/regexec.c 2003-03-09 14:07:31.000000000 +0200
+++ regexec.c 2003-03-16 07:26:12.000000000 +0200
@@ -2832,13 +2832,11 @@ S_regmatch(pTHX_ regnode *prog)
dSP;
OP_4tree *oop = PL_op;
COP *ocurcop = PL_curcop;
- PAD *old_comppad;
SV *ret;
n = ARG(scan);
PL_op = (OP_4tree*)PL_regdata->data[n];
DEBUG_r( PerlIO_printf(Perl_debug_log, " re_eval 0x%"UVxf"\n", PTR2UV(PL_op)) );
- PAD_SAVE_LOCAL(old_comppad, (PAD*)PL_regdata->data[n + 2]);
PL_regendp[0] = PL_reg_magic->mg_len = locinput - PL_bostr;
{
@@ -2854,7 +2852,6 @@ S_regmatch(pTHX_ regnode *prog)
}
PL_op = oop;
- PAD_RESTORE_LOCAL(old_comppad);
PL_curcop = ocurcop;
if (logical) {
if (logical == 2) { /* Postponed subexpression. */
--- /arc/perl-current/pp_ctl.c 2003-03-05 01:37:58.000000000 +0200
+++ pp_ctl.c 2003-03-16 05:42:59.000000000 +0200
@@ -2810,10 +2815,10 @@ S_doeval(pTHX_ int gimme, OP** startop,
/* set up a scratch pad */
- CvPADLIST(PL_compcv) = pad_new(padnew_SAVE);
-
-
- SAVEMORTALIZESV(PL_compcv); /* must remain until end of current statement */
+ if (!startop) {
+ CvPADLIST(PL_compcv) = pad_new(padnew_SAVE);
+ SAVEMORTALIZESV(PL_compcv);
+ }
/* make sure we compile in the right package */
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