Hashes are defined to take string keys (though...stringification can make that work for random objects sometimes depending on what you expect of the value later; for just finding the object, and if the default stringification is unique among all such objects, it works).

I tried a weird thing, using lists as a hash key, and got remarkable results; Data::Dumper is claiming my hash has 3 members with the same key!

It was just playing around, and I don't see any important use for it (if I did, I'd need to understand it enough to really believe in it!; now I'm just a little curious).

This code:

use Data::Dumper;
my %h1;

$h1{(1, 1)} = 17;
$h1{(2, 2)} = 19;
$h1{('', 22)} = 23;
$h1{(22, '')} = 22;
my @h = (3, 4, 5);
$h1{(@h)} = 44;
print Dumper(\%h1);
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Produces this output:

$VAR1 = {
          '22' => 22,
          '22' => 23,
          '11' => 17,
          '3' => 44,
          '22' => 19
        };
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(I observed this with perl 5, version 32, subversion 1 (v5.32.1) built for amd64-freebsd-thread-multi; I believe it's the default FreeBSD binary currently. So not an obscure environment.)