On Nov 5, 2011, at 9:59 AM, Lasse Reichstein wrote:
> On Sat, Nov 5, 2011 at 5:28 PM, Allen Wirfs-Brock <al...@wirfs-brock.com>
> wrote:
>> In the following declaration, what should be the value of z?
>>
>> let [z,y,z] = {0:0, 1:1, length: 2, 2:2};
>
> (I assume the pattern should be [x,y,z], not [z,y,z], or am I missing a
> point?)
oops...
>
>> should it be be 2 or undefined
>
> If it does anything at all (and not, say, throw a TypeError because
> the RHS isn't an Array, which it won't), I'd go for 2.
>
> There is no reason to involve RHS.length at all. The LHS isn't an
> array, why should it require array-like-ness of the RHS. The LHS
> together with the assignment operator is a construct that binds the
> properties "0", "1", and "2" of the object on the RHS to the variables
> "x", "y", and "z". It should be equivalent to the pattern {0:x, 1:y,
> 2:z}.
then what are the rules if ... is used on the LHS.
>
> What if the RHS doesn't have a length property at all? Or it has one
> with a value that isn't convertible to a number? No need for that
> complexity.
This case is consistently handled throughtout the ES spec:
ToInteger( obj.[[Get]]("length"))
evaluates to 0 if length is missing or has a bogus value.
>
>> undefined might be reasonable because it is an array pattern, and the source
>> object is only has two "array-like" elements
>> 2 might be reasonable because the source object actually has a property
>> named "2"
>>
>> Which alternative will be least surprising to JS programmers?
>
> Mine, obviously. At least the least surprising to me.
> I've learned not to generalize from that.
>
> /L
>
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