>>> Just to start with, what does this mean:
>>>
>>> [a,b,...r,c,d = [1,2,3]
>>
>> That seems related to
>> [a, b, c, d] = [1,2,3]
>> and to
>> [a,b,...r,c,d] = [1,2,3,4]
>>
>> Hence, I would guess:
>> a === 1
>> b === 2
>> r === []
>> c === 3
>> d === undefined
>
> Why guess?
I’m not sure I understand.
> There is no requirement that ...r consume 1 element,
It consumes 0 elements above.
> but there is a requirement in Dave's desugaring that trailing non-rest
> element patterns consume elements up to the one indexed by rhs.length - 1.
But that doesn’t help if there are more trailing elements in the pattern than
in the array to be destructured.
My definition would be:
[a1, ⋯ , an, ...r, b1, ⋯, bm] = [c1, ⋯, cl]
- n+m > l: r is bound to [], the non-rest pattern variables are bound as if
there was no rest element:
[a1, ⋯ , an, b1, ⋯, bm] = [c1, ⋯, cl]
- Otherwise r is bound to an array [r1, ⋯, rk] (with k = l-(n+m)) whose
elements are determined via
[a1, ⋯ , an, r1, ⋯, rk, b1, ⋯, bm] = [c1, ⋯, cl]
--
Dr. Axel Rauschmayer
a...@rauschma.de
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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