Agreed. This is easy to spec and implement, highly composable (it fits neatly
into the algebra of destructuring patterns everywhere, as opposed to just in
object property-name positions), has no problems with side effects, and does
not violate restrictions that IINM strict mode is supposed to ban (repeated
property names in literals).
The repeated property-name thing is a hack. It does not Say What You Mean (it's
a total surprise). It is not composable (it only works for property names, not
for array indices).
Worst of all, it will trigger getters twice:
> let { b, b: { x, y } } = { get b() { console.log("BOO!"); return 17 } }
BOO!
BOO!
But if that's the only way to do it, then if you want to destructure a getter,
you will be forced not to use the hack, and to bind a temporary variable and do
a second destructuring on a second line.
*Please*, let's do this right. There's no reason to introduce hacks. I'm open
to various syntaxes, but I think `as` is nice especially because it could work
well for import/export syntax too. Lots of people complain about confusion over
which is the bound name and which is the label. IINM, we could allow both:
let { x: x as y } = obj;
and
let { x as y } = obj;
which would be a nice idiom for making it more obvious that x is the label and
y is the binding. Then this would be especially nice for imports:
import { x as y } from X;
Dave
On Apr 18, 2012, at 8:57 AM, Andreas Rossberg wrote:
> On 18 April 2012 17:51, Herby Vojčík <he...@mailbox.sk> wrote:
>> Maybe allowing
>> let {b, b:{x,y}} = obj;
>> would be enough. It sort-of comforms to existing syntax as well as
>> semantics.
>
> That won't work for arrays, for example.
>
> I agree that 'as' patterns (and even more so, wildcard patterns) are
> basic building blocks that are currently missing. They are extremely
> useful in practice, for a very small price -- i.e., they are trivial
> to spec and implement, (unlike callable objects, because Brendan just
> mentioned those :) ).
>
> /Andreas
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