Allen Wirfs-Brock wrote:
On Apr 18, 2012, at 1:45 PM, Herby Vojčík wrote:
Brendan Eich wrote:
Allen Wirfs-Brock wrote:
For array patterns we would need to allow property assignments in
array literals:
let [b, 0:{x,y}] = ...;
This was proposed at one point, IIRC, but a while ago.
Of course, one could destructure like so:
let {0: b, 0: {x, y}} = ...;
It was also suggested that we allow iterators/generators to supply the
initialization values to array destructurings. This currently isn't in
the draft spec. and I think it would introduce some fairly significant
specification and practical complications (eg, rest bindings and
open-ended generators).
Destructuring patterns should be static. I don't see a conflict if we
stick to this rule, but given the ability to use an object pattern, I
don't see a need for the array literal element label syntax either.
As was already pointed out, problems are not only _array_ destructurings, but
more argument list destructrings, where if you want to destructure 0-th
argument both as b and as {x,y}, you would need something like that, since you
already are inside list, you cannot opt for object.
function f({b},...rest) {
let {x,y}=b;
...
}
doesn't seem like too much of a burden
It was an example to show the problem in principle, it's not that this
concrete example is the problem... if you use object destructuring on
array, you cannot use spread to catch the rest - and on the other hand,
if you use array destructuring, you must then do additional let's like
the one before.
Not a big problem, but it would be nicer if these compromises would not
need to be there.
Possible solution for both object and array destructing at the same time
would be to allow use comma-expression-like destructurings:
let {b:(b,{x,y})} = obj;
let [(b,{x,y}), ...rest] = [obj, ...];
function f((b,{x,y}),foo,bar) { ... }
The object notation is nicer and more readable imo, but this solves the
problem for any destructuring.
Allen
Herby
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