SpeciesConstructor(o, %Set) vs. %Set%

# Michał Wadas (6 years ago)

This is question directed more to TC39 members. I'm updating Set methods proposal right now and I don't understand when SpeciesConstructor should be used and when I should just hardcode %Set%.

Michał Wadas

Hi.

This is question directed more to TC39 members. I'm updating Set methods
proposal right now and I don't understand when SpeciesConstructor should be
used and when I should just hardcode %Set%.

Michał Wadas
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# Jordan Harband (6 years ago)

My sense is that any time you want to enable subclassing, you'd use SpeciesConstructor - are there specific cases where you're seeing it not be used?

My sense is that any time you want to enable subclassing, you'd use
SpeciesConstructor - are there specific cases where you're seeing it not be
used?

On Thu, Dec 13, 2018 at 12:06 PM Michał Wadas <michalwadas at gmail.com> wrote:

> Hi.
>
> This is question directed more to TC39 members. I'm updating Set methods
> proposal right now and I don't understand when SpeciesConstructor should be
> used and when I should just hardcode %Set%.
>
> Michał Wadas
> _______________________________________________
> es-discuss mailing list
> es-discuss at mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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# Kevin Gibbons (6 years ago)

That is an excellent question; see tc39/ecma262#1313 . I would lean towards using SpeciesConstructor because it is consistent with the language as currently defined, and we have not gotten consensus to decide on a different design.

It's pretty unfortunate because it seems likely that very few people will ever benefit from subclassing Set but every visitor of every webpage which uses one of these methods during first load will have to pay the price of several observable property lookups, but what can you do. That's already true for anyone using .map on an array or .then on a promise.

That is an excellent question; see
https://github.com/tc39/ecma262/issues/1313 . I would lean towards using
SpeciesConstructor because it is consistent with the language as currently
defined, and we have not gotten consensus to decide on a different design.

It's pretty unfortunate because it seems likely that very few people will
ever benefit from subclassing Set but every visitor of every webpage which
uses one of these methods during first load will have to pay the price of
several observable property lookups, but what can you do. That's already
true for anyone using `.map` on an array or `.then` on a promise.

On Thu, Dec 13, 2018 at 1:13 PM Jordan Harband <ljharb at gmail.com> wrote:

> My sense is that any time you want to enable subclassing, you'd use
> SpeciesConstructor - are there specific cases where you're seeing it not be
> used?
>
> On Thu, Dec 13, 2018 at 12:06 PM Michał Wadas <michalwadas at gmail.com>
> wrote:
>
>> Hi.
>>
>> This is question directed more to TC39 members. I'm updating Set methods
>> proposal right now and I don't understand when SpeciesConstructor should be
>> used and when I should just hardcode %Set%.
>>
>> Michał Wadas
>> _______________________________________________
>> 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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