[+google-caja-discuss]
I don't see any problems for SES. cc'ing google-caja-discuss in case
someone there spots something I missed. Anyone?
Assuming there are no problems, I like this for all the reasons stated.
On Tue, Feb 26, 2013 at 11:22 AM, Brendan Eich <bren...@mozilla.com> wrote:
> Claude Pache wrote:
>
>> An alternative to a writable 'length' property, is to make it
>> configurable and nonwritable. It would prevent the issue of accidental
>> assignments to the 'length' property that used be ignored in non-strict
>> mode (they'll still be ignored), but it would allow to modify its value
>> using Object.defineProperty.
>>
>
> That's not half-bad.
>
> I used to tell Allen I saw no purpose in non-writable but configurable,
> but against the backdrop of JS history, I see it.
>
> Mark, does this cause SES problems?
>
> /be
>
>
>> —Claude
>>
>> Le 25 févr. 2013 à 07:27, Nathan Wall<nathan.w...@live.com> a écrit :
>>
>> Would it be possible to make / what are the thoughts on making `length`
>>> mutable on functions?
>>>
>>> Writing to `length` could be a useful functionality for library code.
>>> For instance, implementing something like `bind` correctly requires the
>>> arity of the bound function to be the same as the original function minus
>>> the number of preloaded arguments.
>>>
>>> Simplified example:
>>>
>>> var slice = Function.prototype.call.bind(**Array.prototype.slice);
>>> function bind(f, thisArg, ...args) {
>>> function bound() {
>>> return f.apply(thisArg, args.concat(slice(arguments)))**;
>>> }
>>> var L = f.length - args.length;
>>> bound.length = L> 0 ? L : 0;
>>> return bound;
>>> }
>>>
>>> Of course, `bind` is already on Function.prototype, so an ES6 library
>>> has no need to implement it. I'm only using bind as an example to establish
>>> precedent that writable `length` could be useful in implementing function
>>> wrappers. Consider as a more necessary example implementing an
>>> `uncurryThis` function.
>>>
>>> var uncurryThis = Function.prototype.bind.bind(**
>>> Function.prototype.call);
>>> function foo(a, b, c) { /* ... */ }
>>> var uFoo = uncurryThis(foo);
>>> console.log(
>>> foo.length, // => 3
>>> uFoo.length // => 1
>>> );
>>>
>>> This is problematic because we lose information about the arity of the
>>> `uFoo` function which actually takes 4 arguments now: A `this` argument,
>>> `a`, `b`, and `c`. A simple solution would be to write an uncurryThis
>>> which corrects the arity:
>>>
>>> var bind = Function.prototype.call.bind(**Function.prototype.bind),
>>> callMethod = Function.prototype.call;
>>> function uncurryThis(fn) {
>>> var F = bind(callMethod, fn);
>>> // Correct arity.
>>> F.length = fn.length + 1;
>>> return F;
>>> }
>>> function foo(a, b, c) { /* ... */ }
>>> var uFoo = uncurryThis(foo);
>>> console.log(
>>> foo.length, // => 3
>>> uFoo.length // => 4
>>> );
>>>
>>> Currently I have resorted to an `eval` based solution for creating
>>> wrapper functions which are defined with the correct number of arguments
>>> when a certain arity is desired. Obviously this is not ideal. Writable
>>> `length` would help a lot.
>>>
>>> Thoughts?
>>>
>>> Nathan
>>
>>
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