Function length

[Mariusz Nowak]

I find Function 'length' as very useful property (I use it in some low-level
functional stuff). I also think that defining functions so it reflects only
required arguments is very sane decision. In that light I would also expect
...rest to not be counted in Function length.

+1 for keeping it, the way it is.


Brendan Eich-2 wrote:
> 
> I would not mind removing Function 'length' but on the web you cannot 
> deprecate and any browser daring to remove will appear broken to users 
> not involved in the content or the engine, and users switch browsers.
> 
> Anyway, back to reality: foo.length is in ECMA-262 and we need to spec 
> how it works in the presence of a trailing rest parameter. Allen has 
> drafted something based on discussion here. It's a plausible design and 
> hard to criticize without both your use-case (in detail) and a better 
> alternative.
> 
> /be
> 
> Irakli Gozalishvili wrote:
>>> I don't think any library should ever rely on f.length. 
>>
>> That's a wrong  attitude, there always will be legitimate uses of any 
>> feature, otherwise such features are just harmful & IMO should  be 
>> deprecated / removed.
>>
>>> It is not a
>>> reliable source of information (f might use 'arguments' even when the
>>> length is officially 0), and I don't honestly see it being useful for
>>> anything but tertiary debugging purposes.
>>
>> In some cases weather function captures `rest` arguments via 
>> `arguments` is irrelevant. Like in a case I've pointed out earlier. 
>> Library provides arity based dispatch based on f.length, so if you 
>> pass `function() { arguments…. }` it will never be called with more 
>> than 0 arguments.
>>
>> Regards
>> --
>> Irakli Gozalishvili
>> Web: http://www.jeditoolkit.com/
>>
>> On Monday, 2012-06-11 at 05:33 , Andreas Rossberg wrote:
>>
>>> On 10 June 2012 03:52, Irakli Gozalishvili <rfobic at gmail.com 
>>> <mailto:rfobic at gmail.com>> wrote:
>>>> I just noticed strange behavior in spider monkey implementation of rest
>>>> arguments:
>>>>
>>>> (function(a, b, ...rest) {}).length // => 2
>>>>
>>>> I think ignoring `rest` in length is pretty counter intuitive. For 
>>>> example I
>>>> have small utility function that
>>>> I use to dispatch depending on argument length.
>>>>
>>>> var sum = dispatcher([
>>>>   function() { return 0 },
>>>>   function(x) { return x },
>>>>   function(x, y) { return x + y },
>>>>   function(x, y, z) { return Array.prototype.slice.call(arguments,
>>>> 1).reduce(sum, x) }
>>>> ])
>>>
>>> I don't think any library should ever rely on f.length. It is not a
>>> reliable source of information (f might use 'arguments' even when the
>>> length is officially 0), and I don't honestly see it being useful for
>>> anything but tertiary debugging purposes.
>>>
>>> /Andreas
>>
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-----
Mariusz Nowak

https://github.com/medikoo
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