In A Scalar::Util::refaddr Oddity, I discussed a failure mode of pure-perl refaddr($), and ambrus pointed out another in his reply to that node.

1. An unblessed reference becomes blessed when refaddr($) is called on it.
2. A reference to a literal constant causes refaddr($) to die with a "Modification of constant" error.

A proposed fix:

sub refaddr($) {    
    my $pkg = ref($_[0]) or return;
    my $is_object = Scalar::Util::blessed($_[0]);

    bless $_[0], 'Scalar::Util::Fake' if $is_object;
  
    my $i = int($_[0]);

    bless $_[0], $pkg if $is_object;

    $i;
}
[download]

That probably works for anything. I hedge that statement a little because some XS wizard might find a way to bless a literal constant.