for statement with index and value

[Edwin Reynoso]

So I'm assuming this would be special to arrays??

because destructuring works fine for anything that's iterable:

meaning how would it know what to take out for Sets??

```JS
for(let value, index of [1,2]) {
 // do something
}
```

With destructuring we at least know what's being extracted (not sure if
destructured would be the right word, clueless on that):

```JS
let it = [1,2].entries();
let [index, value] = it.next();
// same as:
let [index, value] = [0, 1];
// the matching is obvious
```

With your suggestion it's not obvious:

```JS
for(let value, index of [1,2]) // how does it know what value and index
would be??
```

I don't think this would be done if it's only for Arrays.

On Tue, Jul 14, 2015 at 12:04 AM, Tingan Ho <tingan87 at gmail.com> wrote:

> >Unfortunately we can't have both...
> ```
> for (let [index, value] of values){
> ```
>
> I was suggesting the syntax:
> ```
> for (let value, index of values){
> ```
> `value` comes first and no `[ ... ]`.
>
>
>
> On Tue, Jul 14, 2015 at 11:52 AM, Logan Smyth <loganfsmyth at gmail.com>
> wrote:
>
>> Unfortunately we can't have both
>>
>> ```
>> for (let value of values){
>> ```
>>
>> and
>>
>> ```
>> for (let [index, value] of values){
>> ```
>>
>> Over all, the first one is the more likely one on a day-to-day basis.
>>
>> The `[]` are needed because the `for...of` follows the standard rules for
>> assignment, so it uses standard destructuring, and JS array destructuring
>> requires `[]`.
>>
>> ```
>> for (let [index, value] of values.entries()){
>> ```
>>
>> is essentially is the same as
>>
>> ```
>> for (let pair of values.entries()){
>>     let [index, value] = pair;
>> ```
>>
>> As for your last question, `.entries` returns an iterator, so it will not
>> create a copy of the array.
>>
>> On Mon, Jul 13, 2015 at 7:43 PM, Tingan Ho <tingan87 at gmail.com> wrote:
>>
>>> >for (let [index, value] of [1, 2, 3].entries())
>>>         console.log(index + ": " + value)
>>>
>>> I still think most people will write:
>>>
>>> ```
>>> for (let value of values) { ... }
>>> ```
>>> and then rewrite the whole expression inside the `for-loop` when they
>>> find out that they need the index too:
>>> ```
>>> for (let [index, value] of [1, 2, 3].entries())
>>>         console.log(index + ": " + value)
>>> ```
>>> `for (let value, index of values) { ... }` is still much easier to type
>>> than `for (let [index, value] of [1, 2, 3].entries())` and also more
>>> readable.
>>>
>>>
>>> Also, doesn't that makes a copy of the `[1, 2, 3]`?
>>>
>>> --
>>> Sincerely,
>>>
>>> Tingan Ho
>>> @tingan87 <https://twitter.com/tingan87>
>>>
>>> _______________________________________________
>>> es-discuss mailing list
>>> es-discuss at mozilla.org
>>> https://mail.mozilla.org/listinfo/es-discuss
>>>
>>>
>>
>
>
> --
> Sincerely,
>
> Tingan Ho
> @tingan87 <https://twitter.com/tingan87>
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
>
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