From mike@tecc.co.uk

#!/usr/bin/perl -w

# I'm using perl version 5.004_04 built for sun4-solaris
# The manual (man perlfunc) says​:
#
# There is a single iterator for each hash, shared by all
# each(), keys(), and values() function calls in the program
#
# But the following program appears to prove this false, by working
# correctly in producing all nine possible (key,key) pairs. (Not that
# this is exactly a problem, but it is a surprise.)

use strict;

my %hash = (foo => "fish",
  bar => "bat",
  baz => "bathtub");

foreach my $i (keys %hash) {
  foreach my $j (keys %hash) {
  print("$i,$j\n");
  }
}

Site configuration information for perl 5.00404​:

Configured by stuart at Wed Jan 14 11​:34​:01 GMT 1998.

Summary of my perl5 (5.0 patchlevel 4 subversion 4) configuration​:
  Platform​:
  osname=solaris, osvers=2.6, archname=sun4-solaris
  uname='sunos handbag.tecc.co.uk 5.6 generic sun4u sparc sunw,ultra-2 '
  hint=recommended, useposix=true, d_sigaction=define
  bincompat3=y useperlio=undef d_sfio=undef
  Compiler​:
  cc='gcc -B/usr/ccs/bin/', optimize='-O', gccversion=2.7.2.3
  cppflags='-I/usr/local/include'
  ccflags ='-I/usr/local/include'
  stdchar='unsigned char', d_stdstdio=define, usevfork=false
  voidflags=15, castflags=0, d_casti32=define, d_castneg=define
  intsize=4, alignbytes=8, usemymalloc=y, prototype=define
  Linker and Libraries​:
  ld='gcc -B/usr/ccs/bin/', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib /usr/ccs/lib
  libs=-lsocket -lnsl -ldl -lm -lc -lcrypt
  libc=/lib/libc.so, so=so
  useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags=' '
  cccdlflags='-fpic', lddlflags='-G -L/usr/local/lib'

Locally applied patches​:
 

@​INC for perl 5.00404​:
  /usr/local/lib/perl5/sun4-solaris/5.00404
  /usr/local/lib/perl5
  /usr/local/lib/perl5/site_perl/sun4-solaris
  /usr/local/lib/perl5/site_perl
  .

Environment for perl 5.00404​:
  HOME=/export/home/staff/mike
  LANG (unset)
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/export/home/staff/mike/bin​:/usr/local/bin​:/usr/bin​:/usr/X/bin​:/usr/ccs/bin​:.
  PERL_BADLANG (unset)
  SHELL=/usr/local/bin/bash

From [Unknown Contact. See original ticket]

Mike Taylor <mike@​tecc.co.uk> writes​:

This is a bug report for perl from mike@​tecc.co.uk,
generated with the help of perlbug 1.20 running under perl 5.00404.

#!/usr/bin/perl -w

# I'm using perl version 5.004_04 built for sun4-solaris
# The manual (man perlfunc) says​:
#
# There is a single iterator for each hash, shared by all
# each(), keys(), and values() function calls in the program
#
# But the following program appears to prove this false, by working
# correctly in producing all nine possible (key,key) pairs. (Not that
# this is exactly a problem, but it is a surprise.)

Yes, but in _current_ perls when you use keys %hash in a foreach
the itterator is use to build a complete list on the stack before
the body is called. We have started optimizing this behaviour (
i.e. avoiding building the full list) but have only done n..m style
so far.

If you recast your example :

use strict;

my %hash = (foo => "fish",
  bar => "bat",
  baz => "bathtub");

while (defined(my $i = each %hash)) {
  while (defined(my $j = each %hash)) {
  print("$i,$j\n");
  }
}

You will see the documented behaviour. foreach _may_ behave
like that someday - but there is a lot of code that uses
foreach (keys %hash) so we may never dare break it ...

--
Nick Ing-Simmons