mg_overload_table.pl

package Z;
use Devel::Peek ();
use overload "+"=>sub {42};
die "fail" unless 42 == bless({}) + 1;

Devel::Peek::Dump \%Z::;
use Inline C => <<END;
void foo(SV* targ) {
    if (!SvOK(targ)) return;
    if (SvROK(targ)) targ = SvRV(targ);

    if (SvMAGICAL(targ) && mg_find(targ, PERL_MAGIC_overload_table)) {
        warn("sv_unmagic");
        sv_unmagic(targ, PERL_MAGIC_overload_table);
    }
}
END

foo(\%Z::);
Devel::Peek::Dump \%Z::;

die "fail" unless 42 == bless({}) + 1;