Does Perl know how a particular hash will be ordered ahead of time, given it's characteristics?

I think the answer is yes. I even suspect that Perl uses the same hashing function/algorithm regardless the type/nature of the search key.

I have constructed the following code to test my hypothesis -

my %hashA;
$hashA{123456} = 1;
$hashA{'Roger and Albert'} = 1;
$hashA{'Roger'} = 1;
$hashA{'456789'} = 1;

print "HASH A\n------\n";
print "$_\n" for keys %hashA;

my %hashB;
$hashB{'Roger'} = 1;
$hashB{123456} = 1;
$hashB{'Roger and Albert'} = 1;
$hashB{456789} = 1;

print "\nHASH B\n------\n";
print "$_\n" for keys %hashB;
[download]

And the order of both hashA and hashB are identical -

HASH A
------
456789
123456
Roger and Albert
Roger

HASH B
------
456789
123456
Roger and Albert
Roger
[download]

In the first case, a number is used as a search key to start the hash, while in the second case, a string is used as a search key to start the hash. If the perl hash engine differentiate numeric search keys and string search keys, then I would get two different hash orders for the hashes. But that's not the case.

The conclusion is that Perl treats all the search keys as strings, and it has a single hashing function optimized for string search keys.

However Perl might implement different hashing functions between different versions. Perl 5.8.1 might have introduced a different random seed/number every session to initialize its hashing engine/function, perhaps to reduce the bias of the hashing function and improve the overall performance of the hash.