Check whether your hash keys have random order

[liz]

The subroutine is_hash_randomized() allows you to check whether the hash keys in your Perl have a random or repeatable order (as returned by each or keys. By default, in Perl 5.8.1, the order of hash keys is no longer repeatable: it will be different for each run of Perl.

The subroutine returns either a defined or an undefined value. If an undefined value is returned, then the order of hash keys is not repeatable. If a defined value if returned, it indicates the hash seed that was used to generate, and thereby order, the hash keys.

When called with a Perl < 5.8.1, the value "0" is always returned. Please note though, that the same value only guarantees repeatable hash key order only for a given version of Perl, not for different Perl versions.

Update:
Ok, that's all pretty forgettable. Perl 5.8.1 will have the the hash_seed() subroutine in the Hash::Util module. From the new pod:

hash_seed

my $hash_seed = hash_seed();

hash_seed() returns the seed number used to randomise hash ordering. Zero means the "traditional" random hash ordering, non-zero means the new even more random hash ordering introduced in Perl 5.8.1.

It should be noted that this routine has slightly different semantics, as you can not discover whether you would or would not got different hash key orders for different runs of Perl. But it doesn't need to do any strange things, it's going directly at the Perl internals.

sub is_hash_randomized {

# We don't have any random sequences yet, as if seed "0"

    return 0 if $] < 5.008001;

# Get the -Accflags= settings using this Perl executor

    open my $handle, "$^X -V:ccflags |"
     or die "Could not execute $^X -V:ccflags: $!\n";
    my $ccflags = <$handle>;
    close $handle;

# Return repeatable default if random sequences compiled out
# Return random if switch settings reversed and environment variable s
+et
# Return whatever the environment variable indicates

    return 0 if $ccflags =~ m#-DNO_HASH_SEED#;
    return   if $ccflags =~ m#-DUSE_HASH_SEED_EXPLICIT#
                 and exists $ENV{PERL_HASH_SEED};
    $ENV{PERL_HASH_SEED};
} #is_hash_randomized