IsConstructor

[Allen Wirfs-Brock]

On Jun 11, 2014, at 11:59 AM, Rick Waldron wrote:

> 
> 
> 
> On Wed, Jun 11, 2014 at 1:37 PM, Domenic Denicola <domenic at domenicdenicola.com> wrote:
> It's also deceptive: it makes you think `Array.of` and `Array.from` are functions, when in reality they are definitely methods.
> 
> Yes, you're right.
> 
> 
> What about Array subclasses? `from` and `of` are "inherited" when Array is subclassed, so these: 
> 
> 22.1.2.3 4 & 5 (http://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.of)
> 22.1.2.1 8.a & 8.b (http://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.from)
> 22.1.2.1 13 & 14 
> 
> Which are are how `from` and `of` determine what to construct, will be replaced with a single step, being one of:
> 
> Let A be the result of calling the [[Construct]] internal method of C with an empty argument list.
> Let A be the result of calling the [[Construct]] internal method of C with an argument list containing the single item len.
> 
> But surely this step will also have to be guarded by IsCallable(this), which that means this: 
> 
> If IsConstructor(C) is true, then
>   Let A be the result of calling the [[Construct]] internal method of C with an empty argument list.
> Else,
>   Let A be ArrayCreate(0).
> 
> Becomes: 
> 
> If IsCallable(C) is true, then

that's not an adequate guard, be an object can be callable but not have a [[Construct]] internal method so the next step not be valid

>   Let A be the result of calling the [[Construct]] internal method of C with an empty argument list.
> Else,
>   Let A be ArrayCreate(0).

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