ObjectSpace.internal_class_of

static VALUE
objspace_internal_class_of(VALUE self, VALUE obj)
{
    VALUE klass;

    if (rb_typeddata_is_kind_of(obj, &iow_data_type)) {
        obj = (VALUE)DATA_PTR(obj);
    }

    if (RB_TYPE_P(obj, T_IMEMO)) {
        return Qnil;
    }
    else {
        klass = CLASS_OF(obj);
        return wrap_klass_iow(klass);
    }
}