for statement with index and value

[Edwin Reynoso]

Something wrong with server that doesn't let me edit.

But what I meant by the first code snippet was:

```JS
for(let a, b of new Set([1,2])) // what would `a` and `b` be here? How
would it know what to extract??
```
Would `b` just be `undefined`, yet for an array it returns the `index` how
does it determine that unless again this is special to Arrays?? because
`b/index` could be anything else,  that's not obvious compare to
destructuring.


On Tue, Jul 14, 2015 at 12:13 AM, Edwin Reynoso <eorroe at gmail.com> wrote:

> 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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