AV *                    T_AVREF
INPUT
T_AVREF
        if (SvROK($arg) && SvTYPE(SvRV($arg))==SVt_PVAV)
            $var = (AV*)SvRV($arg);
        else
            Perl_croak(aTHX_ \"$var is not an array reference\")
OUTPUT
T_AVREF
        $arg = newRV((SV*)$var);