!Re: proposal: Object Members

[Isiah Meadows]

If you go back a few months, what you're proposing is *very* similar,
at least functionally, to my previous iteration of my proposal:
https://github.com/isiahmeadows/private-symbol-proposal/blob/c5c9781d9e76123c92d8fbc83681fdd3a9b0b319/README.md

My main problem was that trying to limit private properties to objects
created within a scope got complicated in a hurry once you considered
all the small details, and it just didn't seem simple anymore. It only
got more complicated when you started getting into the logistics of
integrating with modules.

So I've considered the issue and explored it pretty thoroughly - I
*really* don't want private data to be limited to classes (which I
dislike), but I did also previously have the concern of trying to
limit who could define properties where.

I will point out that you can prevent arbitrary private extension by
simply doing `Object.preventExtensions(object)`. Because properties
defined using private symbols are otherwise just normal properties,
they still have to go through the same access checks normal properties
have to, like [[IsExtensible]]. The only other concrete difference is
that proxy hooks don't fire when you do things with private symbols.

-----

Isiah Meadows
contact at isiahmeadows.com
www.isiahmeadows.com


On Tue, Jul 31, 2018 at 3:09 PM, Ranando King <kingmph at gmail.com> wrote:
>> What use case are you referring to here?
>
> In the case of SymbolTree, the objects in use are external.
>
>> I think there’s been a misunderstanding. Everybody agrees that that’s a
>> bad pattern. It’s not what the point of private symbols would be. It’s not a
>> target use case.
>
> That certainly puts my mind at ease.
>
>> As Isiah said, “all of the examples here I've presented are for scenarios
>> where the state is related to the factory that created the objects.”
>
> If the factory that creates the objects is the also the only thing trying to
> store private information on those objects, then I understand you're only
> looking for per-instance module-private data, possibly with the ability to
> use common private names. If that's the case, then it really is just 2
> simple extensions of my proposal:
> * allow a Symbol when used as a private or protected property name to
> persist as the private Symbol name for the private instance field on each
> object for which it is used.
> * create an additional privilege level (internal) that places the new
> field's name in the [[DeclarationInfo]] of the function containing the
> declaration.
>
> The effect of using these 2 features together is that anything within the
> same function as the declared Symbol will gain access to the internal field
> of all objects using that Symbol as a field name.
>
> On Tue, Jul 31, 2018 at 1:36 PM Darien Valentine <valentinium at gmail.com>
> wrote:
>>
>> > I'd say you've identified the common pattern, but that pattern itself is
>> > a bad use case, and the use of private symbols as you have defined them
>> > doesn't do anything to correct the technical issue.
>>
>> I think there’s been a misunderstanding. Everybody agrees that that’s a
>> bad pattern. It’s not what the point of private symbols would be. It’s not a
>> target use case.
>>
>> > Since you cannot stick new properties onto a non-extensible object, even
>> > private symbols won't solve the problem with your use case.
>>
>> That appending private symbols to external objects which are frozen
>> wouldn’t work doesn’t matter precisely because it’s not a target use case.
>> That it doesn’t work reliably might even be considered a positive, since it
>> discourages something we all seem to agree is not good practice.
>>
>> It’s also not related to private symbols; this is already how properties
>> work, regardless of what kind of key they have.
>>
>> > The difference here is that in your use cases, library A is "sneakily"
>> > storing information on object B.
>>
>> What use case are you referring to here? I can’t find any example in the
>> previous posts that matches these descriptions. As Isiah said, “all of the
>> examples here I've presented are for scenarios where the state is related to
>> the factory that created the objects.” The same is true of my examples.
>> Everybody’s on the same page regarding not wanting to add properties to
>> objects their own libraries do not create.