No, `Array.from` never produces a holey array whatsoever; only ever a dense
array.
On Sun, Feb 9, 2020 at 11:08 PM Andrea Giammarchi <
andrea.giammar...@gmail.com> wrote:
> Unfortunately, `Array.from({ length: 4 }, () => whatever)` produces a
> holey array, so that the `.repeat(...)` idea, if capable of packing
> elements in a better way, wouldn't be so terrible, as simplification.
>
> Although, the intent of this proposal was to also grant "shapes" or
> kindness of each entry, same way typed Arrays do, but maybe that would
> require some better primitive, as in `const Shape =
> Object.defineShape(...)` and `Object.createShape(Shape)` or similar.
>
> On Sun, Feb 9, 2020 at 10:01 PM Jordan Harband <ljh...@gmail.com> wrote:
>
>> That already exists - `Array.from({ length: 4 }, () => whatever)` - I
>> assume that the hope is to have an array where it is *impossible* for it to
>> have the wrong "kind" of data, and a userland factory function wouldn't
>> provide that.
>>
>> On Sun, Feb 9, 2020 at 10:39 AM kai zhu <kaizhu...@gmail.com> wrote:
>>
>>> > It's a bit of a mess to create an Array that is not holed and gets
>>> best optimizations [1], and this proposal would like to address that exact
>>> case.
>>>
>>> could the performance issue be resolved more easily with a simple
>>> static-function `Array.repeat(<length>, <repeater>)`?
>>>
>>> ```js
>>> let structuredList;
>>> structuredList = Array.repeat(4, function (ii) {
>>> return {
>>> index: 2 * ii + 1,
>>> tags: []
>>> });
>>> /*
>>> structuredList = [
>>> { index: 1, tags: [] },
>>> { index: 3, tags: [] },
>>> { index: 5, tags: [] },
>>> { index: 7, tags: [] }
>>> ];
>>> */
>>> ```
>>>
>>> the only time i can practically enforce the shape of a "StructuredArray"
>>> is during element-insertion,
>>> and a userland insertion/creation function would be just as effective as
>>> a StructuredArray constructor.
>>>
>>> enforcing shapes during element deletions and updates are going to be
>>> hard
>>> and likely just as confusing with StructuredArray as they are with
>>> regular Array.
>>>
>>> also note that most javascript arrays need to be easily JSON-serialized
>>> for message-passing
>>> over-the-wire (commonly http) to external systems.
>>>
>>> -kai
>>>
>>> On Sat, Feb 8, 2020 at 3:46 AM Andrea Giammarchi <
>>> andrea.giammar...@gmail.com> wrote:
>>>
>>>> > having to retroactively add checks like...
>>>>
>>>> we already have typed arrays in JS so I don't think this would be any
>>>> different
>>>>
>>>> > I _think_ that moderns virtual machines already did these
>>>> optimisations despite there isn't a TypedArray like that.
>>>>
>>>> It's a bit of a mess to create an Array that is not holed and gets best
>>>> optimizations [1], and this proposal would like to address that exact case.
>>>>
>>>> [1] https://v8.dev/blog/elements-kinds
>>>>
>>>>
>>>>
>>>>
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>>>>
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>>>
>>
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