Allen Wirfs-Brock wrote:
On Apr 18, 2012, at 9:29 AM, Brendan Eich wrote:
Herby Vojčík wrote:
Herby Vojčík wrote:
Maybe allowing
let {b, b:{x,y}} = obj;
would be enough. It sort-of comforms to existing syntax as well as
semantics.
BTW, if you use var instead of let, if already works out of the box (in FF11
firebug console; just tried), so why include as if it already is there, albeit
in different form?
We implemented destructuring years ago to implementor- and user-test ES4
proposals. They did not forbid duplicates. That's all.
Nothing normative in experimental Firefox implementation features, of course. You cite
them as "already [there]" and that's true but it doesn't govern what goes into
ES6.
But is also works this way according to the ES6 draft spec. It works with var
because var allows duplicated declarations:
var a=1;
var a=2;
var a=3;
which, from a declaration perspective isn't really any different from
var a=1,a=2,a=3;
However let/const does not:
{ //block level duplicate declaration early error
let b=1;
let b=2;
}
or just
let b=1,b=2 ; //block level duplicate declaration error
var {b,b:{x,y}} = obj; //fine because var declaration static semantics don't
disallow duplicates
{ //avoid any conflicts with the preceeding var
let {b,b:{x,y}} = obj; //block level duplicate declaration
}
But the 'let {b:b, b:{x,y}}' is different beast, it is:
{
let b = {x:1,y:2};
let {x,y} = {x:1,y:2};
}
and there is, imo, no conflict in this.
> You might argue that the second b in the destructuring isn't actually
> introducing a binding for b. However, syntactically it looks like
> one and that is what the static semantic rule is driven off of. If
> we allow that, we would also be allowing:
> let b=somethingElse;
> let {b:{x,y})=obj;
>
> If we want to allow that I'll have to some up with a different way to
But, AFAICT, this should be allowed. The 'b:' from destructuring is
different from 'b' from let. Is the previous code disallowed in current
state?
> specify the static semantics.
>
> Allen
Herby
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