Is `List` really a specification type?

# Axel Rauschmayer (10 years ago)

people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys, people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys

The method [[OwnPropertyKeys]] ( ) of proxy objects returns an actual List to JavaScript code. Does that make sense? I thought it was a specification(-only) type? How an instance is created is vague [1], which is appropriate for a data structure at the specification level, but not for one at the base level. Array seems like a better choice here. Or an iterator.

[1] people.mozilla.org/~jorendorff/es6-draft.html#sec

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys <https://people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys>

The method `[[OwnPropertyKeys]] ( )` of proxy objects returns an actual `List` to JavaScript code. Does that make sense? I thought it was a specification(-only) type? How an instance is created is vague [1], which is appropriate for a data structure at the specification level, but not for one at the base level. `Array` seems like a better choice here. Or an iterator.

[1] https://people.mozilla.org/~jorendorff/es6-draft.html#sec-createlistfromarraylike

-- 
Dr. Axel Rauschmayer
axel at rauschma.de
rauschma.de



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# Claude Pache (10 years ago)

Le 27 nov. 2014 à 16:26, Axel Rauschmayer <axel at rauschma.de> a écrit :

people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys, people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys

The method [[OwnPropertyKeys]] ( ) of proxy objects returns an actual List to JavaScript code. Does that make sense? I thought it was a specification(-only) type? How an instance is created is vague [1], which is appropriate for a data structure at the specification level, but not for one at the base level. Array seems like a better choice here. Or an iterator.

[1] people.mozilla.org/~jorendorff/es6-draft.html#sec-createlistfromarraylike, people.mozilla.org/~jorendorff/es6-draft.html#sec-createlistfromarraylike

Lists are indeed specification-only types, and the result of the [[OwnPropertyKeys]] internal method call is never directly observed by the programmer: it is only used as an intermediate result within algorithms. A List is, I presume, a finite ordered sequence of values.

> Le 27 nov. 2014 à 16:26, Axel Rauschmayer <axel at rauschma.de> a écrit :
> 
> https://people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys <https://people.mozilla.org/~jorendorff/es6-draft.html#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys>
> 
> The method `[[OwnPropertyKeys]] ( )` of proxy objects returns an actual `List` to JavaScript code. Does that make sense? I thought it was a specification(-only) type? How an instance is created is vague [1], which is appropriate for a data structure at the specification level, but not for one at the base level. `Array` seems like a better choice here. Or an iterator.
> 
> [1] https://people.mozilla.org/~jorendorff/es6-draft.html#sec-createlistfromarraylike <https://people.mozilla.org/~jorendorff/es6-draft.html#sec-createlistfromarraylike>
> 


Lists are indeed specification-only types, and the result of the `[[OwnPropertyKeys]]` internal method call is never directly observed by the programmer: it is only used as an intermediate result within algorithms. A List is, I presume, a finite ordered sequence of values.


—Claude


> -- 
> Dr. Axel Rauschmayer
> axel at rauschma.de <mailto:axel at rauschma.de>
> rauschma.de
> 
> 
> 
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> es-discuss mailing list
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# Tom Van Cutsem (10 years ago)

2014-11-27 17:12 GMT+01:00 Claude Pache <claude.pache at gmail.com>:

Lists are indeed specification-only types, and the result of the [[OwnPropertyKeys]] internal method call is never directly observed by the programmer: it is only used as an intermediate result within algorithms. A List is, I presume, a finite ordered sequence of values.

Indeed, user-facing functions convert the List to an Array, see e.g. Reflect.ownKeys: people.mozilla.org/~jorendorff/es6-draft.html#sec-reflect.ownkeys

2014-11-27 17:12 GMT+01:00 Claude Pache <claude.pache at gmail.com>:

> Lists are indeed specification-only types, and the result of the
> `[[OwnPropertyKeys]]` internal method call is never directly observed by
> the programmer: it is only used as an intermediate result within
> algorithms. A List is, I presume, a finite ordered sequence of values.
>

Indeed, user-facing functions convert the List to an Array, see e.g.
Reflect.ownKeys:
<https://people.mozilla.org/~jorendorff/es6-draft.html#sec-reflect.ownkeys>

Cheers,
Tom
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