I've released a module named Array::AsHash which allows one to use references as hash keys (it actually does a lot more than this, but this is one of the features). Normally, this works fine:

my $array = Array::AsHash->new({array => \@array});
my $value = $array->get($some_reference);
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It does this by checking the Scalar::Util::refaddr of the reference. However, this can fail if someone wants to override equality. In Python, you can get around this by overriding the __hash__() method of object. In Perl, we can't do this with unblessed references. Thus, the following will never succeed:

my $aref = [1,2,3];
my $array = Array::AsHash->new({
  array => [ $aref => 'Ovid' ]
});
print $array->get($aref);   # prints "Ovid"
print $array->get([1,2,3]); # fails
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Ordinarily, this is fine. However, if we only care about the values a reference contains and not whether or not it's the same reference, we're stuck. I'd like to be able to pass the constructor a coderef which will determine equality of references beyond simply comparing their addresses. Things like the Test::More::is_deeply function or the useful Test::Deep module would be great, but they're tied to Perl's testing framework.

Can anyone offer suggestions?

For those wondering why I want to do this, I don't need this myself (yet), but I'm creating a flexible general purpose tool for folks and I'd like to give them the ability to override behavior as needed.