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.
allen
_______________________________________________
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss
