New Array Functions

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`~` has a meaning:
http://www.ecma-international.org/ecma-262/8.0/index.html#sec-bitwise-not-operator
`~0` is `-1`. `x[-1]` is accessing the property called `"-1"` in the array
object. (Which it probably doesn't have, but certainly *could* have.)

If you want to propose something else, you'll need to provide some means of
differentiating from existing syntax, since of course breaking existing
syntax is not going to happen.

-- T.J. Crowder

On Tue, Jul 11, 2017 at 6:19 PM, Sebastian Malton <sebastian at malton.name>
wrote:

> Using the ~ to count from the back of the array.
>
> Basically
>
> ```js
> let x = [1,2,3,4,5];
> x[4] === x[~0] === 5; //I know this is not how JS checking works
> ```
>
> Sebastian
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
>
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Unfortunately, what you're proposing is already valid and has a different
behavior:

```javascript
> x = [1, 2, 3, 4, 5];
[ 1, 2, 3, 4, 5 ]
> x[-1] = 'oh no'
'oh no'
> x[~0]
'oh no'
> x[4]
5
```

What about adding a prototype method like `last` to Array instead? With
`[1,2,3].last()` returning 3, `[1,2,3].last(1)` returning 2, etc

Le mar. 11 juil. 2017 à 19:19, Sebastian Malton <sebastian at malton.name> a
écrit :

> Using the ~ to count from the back of the array.
>
> Basically
>
> ```js
> let x = [1,2,3,4,5];
> x[4] === x[~0] === 5; //I know this is not how JS checking works
> ```
>
> Sebastian
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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`array.get(-1)` could have the desired semantics (and be nicely symmetric
with Map), but actually in other languages (e.g. Python) I find that this
"trick" with negative numbers can lead to a surprising (and scary)
propagation of bugs, where array bounds checking is not correctly done.
Actually this exact behaviour caught me^Wsomeone who isn't me out, in
Immutable.js's `List` type already.

On 11 July 2017 at 18:31, Guylian Cox <guyliancox at gmail.com> wrote:

> Unfortunately, what you're proposing is already valid and has a different
> behavior:
>
> ```javascript
> > x = [1, 2, 3, 4, 5];
> [ 1, 2, 3, 4, 5 ]
> > x[-1] = 'oh no'
> 'oh no'
> > x[~0]
> 'oh no'
> > x[4]
> 5
> ```
>
> What about adding a prototype method like `last` to Array instead? With
> `[1,2,3].last()` returning 3, `[1,2,3].last(1)` returning 2, etc
>
> Le mar. 11 juil. 2017 à 19:19, Sebastian Malton <sebastian at malton.name> a
> écrit :
>
>> Using the ~ to count from the back of the array.
>>
>> Basically
>>
>> ```js
>> let x = [1,2,3,4,5];
>> x[4] === x[~0] === 5; //I know this is not how JS checking works
>> ```
>>
>> Sebastian
>> _______________________________________________
>> es-discuss mailing list
>> es-discuss at mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
>
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