Oh wise monks! I am sort of stumped.

I think I see Perl 5.6.1 sorting differently (sometimes) than Perl 5.8.8. (And no, I can't just use 5.8.8.) Specifically, it looks like 5.6.1 has an imperfect notion of keeping "ties" in the order received.

I would greatly appreciate additional eyes on the code below, looking for any stupid mistakes I've made. The really nutty thing is that if I take away the last hashref in @unordered the sucker passes in 5.6.1.

Here's the code:

# show that sorting has changed from 5.6.1 to 5.8.8
use strict;
use warnings;
use Test::More tests => 1;

# I would expect ties to come out in the order in which they are
# received.  5.8.8 seems to do that, 5.6.1 does not.
my @unordered = (

    { pos => 3, val => 0 },
    { pos => 5, val => 1 },
    { pos => 4, val => 0 },
    { pos => 1, val => -1 },
    { pos => 2, val => -1 },
    { pos => 6, val => 1 },
    { pos => 0, val => -2 },

);
my @ordered = sort { $a->{pos} <=> $b->{pos} } @unordered;

my @result = sort { $a->{val} <=> $b->{val} } @unordered;

is_deeply( \@result, \@ordered );

diag("Your Perl is $].");
diag( "expected val: " . join( ",", map { $_->{val} } @ordered ) );
diag( "  result val: " . join( ",", map { $_->{val} } @result ) );
diag( "expected pos: " . join( ",", map { $_->{pos} } @ordered ) );
diag( "  result pos: " . join( ",", map { $_->{pos} } @result ) );
[download]

Here's the output for v5.8.8 built for darwin-2level:

1..1
ok 1
# Your Perl is 5.008008.
# expected val: -2,-1,-1,0,0,1,1
#   result val: -2,-1,-1,0,0,1,1
# expected pos: 0,1,2,3,4,5,6
#   result pos: 0,1,2,3,4,5,6
[download]

And here's the output for v5.6.1 built for i386-linux:

1..1
not ok 1
#   Failed test at wtf.pl line 24.
#     Structures begin differing at:
#          $got->[5]{pos} = '6'
#     $expected->[5]{pos} = '5'
# Your Perl is 5.006001.
# expected val: -2,-1,-1,0,0,1,1
#   result val: -2,-1,-1,0,0,1,1
# expected pos: 0,1,2,3,4,5,6
#   result pos: 0,1,2,3,4,6,5
# Looks like you failed 1 test of 1.
[download]

Of course I'm trying to solve a slightly trickier problem, but this is about as reductive a demonstration as I could come up with. Using a sort subroutine is an option, so if this is a known quirk with a known workaround I'm all ears.

Many thanks in advance for suggestions, reprimands, &c.

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