Slice them arrays!

test.c

void array_range____OP_IDX_T__star_Range__T__star(uint8_t* __genericReturn1, lang_types__Class* T, uint8_t* data, lang_Numbers__Range range) {
    lang_Numbers__Int size = range.max - range.min;
    uint8_t* ret = ((uint8_t*) (lang_Memory__gc_malloc(size * T->size)));
    
    {
        lang_Numbers__Int i;
        for (i = 0; i < size; i++) {
            lang_Memory__memcpy(&(ret[i * T->size]), &(data[(range.min + i) * T->size]), T->size);
        }
    }
    if (__genericReturn1) {
        __genericReturn1 = ret;
    }
    return;
}

// Here is the call to it
array_range____OP_IDX_T__star_Range__T__star((uint8_t*) &(array_range__data), (lang_types__Class*)lang_Numbers__Int_class(), (uint8_t*) array_range__list, lang_Numbers__Range_new(0, 3));
//                                         ^ array_range_data should not be referenced >.<

// With
lang_Numbers__Int* array_range__data;
lang_Numbers__Int* array_range__list;

array_range__list = ((lang_Numbers__Int*) ((lang_Numbers__SSizeT[]) { 0, 1, 2, 3, 4 }));

test.ooc

operator [] <T> (data: T*, range: Range) -> T* {
    size := range max - range min
    ret := gc_malloc(size * T size) as T*
    for(i in 0 .. size) {
        ret[i] = data[(range min + i)]
    }
    ret
}