On Apr 18, 2012, at 9:49 AM, Allen Wirfs-Brock wrote:
> ...
> 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
> }
>
> 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 specify
> the static semantics.
False alarm! Actually the above isn't correct. The current spec draft actually
does allow
let {b,b:{x,y}};
but would issue an early error on
let {b,b:{x:b,y}};
It is all in the static semantics production Bound Names in 12.2.4
The BoundNames of
let {b}=obj
is ["b"]
The BoundNames of
let {b:x} = obj
is ["x"]
The Bound Names of
let {b,b:{x,y}
is ["b","x","y"]
The Bound Names of
let {b,b:{x:b,y}};
is ["b","b","y"] and produces a duplicate declaration early error. For a var
declaration it would be allowd.
Sorry for the confusion. I should have read my own spec. more carefully.
Allen
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