On Nov 21, 2011, at 8:49 AM, Allen Wirfs-Brock wrote:
> On Nov 20, 2011, at 8:30 PM, Brendan Eich wrote:
>
>> On Nov 20, 2011, at 1:18 PM, David Herman wrote:
>>
>>>> I would not add more implicit magic to JS. E4X had junk like this in it,
>>>> which only ever concealed bugs.
>>>
>>> I'm of two minds about this. In the abstract, I agree with Brendan;
>>> fail-soft conceals bugs. But in reality, our destructuring logic is
>>> incredible fail-soft. Hardly anything in destructuring is treated as an
>>> error. And the syntax really *wants* to match the common pattern. So I'm
>>> torn.
>>
>> 1. Failing to write that means a destructuring parameter with default values
>> within the pattern cannot be observed via arguments[i] as undefined (or
>> null?). If missing, the undefined will be replaced by a fresh object. This
>> isn't consistent with any other combination of destructuring parameters and
>> parameter default values.
>
> Actually, I've specified parameter default value initialization such that the
> arguments object is an array of the actual argument values. It contains no
> default value substitutions. Even if function f({a,b}) is interpreted as
> function f({a,b}=undefined) the value of arguments[0] for a call of the form
> f(undefined) would still be undefined.
>
> I'm not particularly in favor of treating undefined/null as { }, but I don't
> think the arguments object is particularly relevant to the issue.
If you had not preserved the actual undefined, I would argue differently. We
all hate arguments but chipping away at consistency involving observations made
using it has a bad smell.
What about points 2 and 3?
/be
_______________________________________________
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss
