NameError#receiver

static VALUE
name_err_receiver(VALUE self)
{
    VALUE recv = rb_ivar_lookup(self, id_recv, Qundef);
    if (!UNDEF_P(recv)) return recv;

    VALUE mesg = rb_attr_get(self, id_mesg);
    if (!rb_typeddata_is_kind_of(mesg, &name_err_mesg_data_type)) {
        rb_raise(rb_eArgError, "no receiver is available");
    }

    name_error_message_t *ptr;
    TypedData_Get_Struct(mesg, name_error_message_t, &name_err_mesg_data_type, ptr);
    return ptr->recv;
}