!Re: proposal: Object Members

[Ranando King]

Thanks for that information. I wasn't yet sure how to handle it. A parallel
question is this: Is there any particular reason that the private container
itself shouldn't be mutable? Or more directly, is there a good reason for
private fields to only be create-able at declaration time? So far, all the
logic I've created hinges on the reference to [[DeclarationInfo]] (which
keeps all the known private names). Since that container is created at
declaration time, it's not unfeasible for private properties to be appended
after the declaration. I'm not particularly fond of the idea, but I'm also
trying not to let my own biases commit me to a decision.

On Tue, Jul 31, 2018 at 4:41 PM Jordan Harband <ljharb at gmail.com> wrote:

> Note that builtins with internal slots, like Map, Set, and Promise, are
> still mutable after being frozen - so if one is trying to model internal
> slots with some kind of property stored on the object, then freezing *must*
> have no effect on the ability to alter their contents.
>
> On Tue, Jul 31, 2018 at 2:34 PM, Isiah Meadows <isiahmeadows at gmail.com>
> wrote:
>
>> 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.
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