An array destructing specification choice

Dmitry Soshnikov dmitry.soshnikov at gmail.com
Sat Nov 5 10:06:11 PDT 2011


On 05.11.2011 21:04, Dmitry Soshnikov wrote:
> On 05.11.2011 20:54, Allen Wirfs-Brock wrote:
>> On Nov 5, 2011, at 9:45 AM, Dmitry Soshnikov wrote:
>>
>>> On 05.11.2011 20:38, Allen Wirfs-Brock wrote:
>>>> In a similar vain, what is the value of r in:
>>>>
>>>> let [z,y,...r] = {0:0, 1:1, 2:2, length: 3, 3:3,4:4};
>>>>
>>>> should it be [2] or [2,3,4]  (and if the latter how is that 
>>>> determined)?
>>>>
>>>> It seems to me that [2] is the right answer,
>>> How so? If `...n` is the range slice operator, it should be [2, 3, 
>>> 4], no?
>> How do you define the range of "array-like elements" of an object.  
>> In all other places of the ES specification, the value of the 
>> "length" property is used to determine the upper bound of the 
>> elements and any "integer keyed" elements beyond the length are 
>> ignored by array operations and functions.
>>
>

Oh! I missed that the `length` is 2! Then yes, it seems it should be 
[2]. Though, have to think on missed properties also.

Dmitry.

> Let's see.
>
> What is the result in case of:
>
> let a = [0, 1, 2, 3, 4];
> a.length = 6;
>
> let [z, y, ...r] = a;
>
> if `...r` depends on the `length` of `a`, then `r` is [2, 3, 4, 
> undefined]; If not, then `r` just takes only existing values (as some 
> array methods do, e.g. forEach or map), and it's [2, 3, 4]. In later 
> case, the simple object semantics obeys this rule.
>
> Dmitry.
>



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