Object id, hash, etc?

Andrea Giammarchi andrea.giammarchi at gmail.com
Wed Sep 9 12:34:56 UTC 2015


Well, to start with, you don't hide symbols, these are all exposed through
`Object.getOwnPropertySymbols` or Reflect.ownKeys so for your use case
looks like using just a non enumerable property would do as well.
And btw, even if Symbols don't show up in for/in and Object.keys, these are
by default also enumerable so Object.assign will copy them around (reason
I've used defineProperty with the value instead of just setting the symbol,
so it's non enumerable by default).

As summary: do you want to be sure that object has a unique "lable" or "id"
associated with it? Use WeakMaps, otherwise be prepared to possible clones
around if some library uses Object.assign thinking that's a good way to
copy properties around.

I still suggest the Labeler approach that Mark previously indicated.

Regards




On Wed, Sep 9, 2015 at 1:15 PM, Michael McGlothlin <
mike.mcglothlin at gmail.com> wrote:

> Using frozen objects and such seems a lot more complex to me than just
> using a property. Using a symbol to hide the property from cluttering seems
> to go along with how other things are being done. And it's my understanding
> that other than hiding it that using a Symbol for a name is nothing special
> - does it have some negative factor that should make using it less
> attractive?
>
> 📱 Michael McGlothlin
>
> On Sep 9, 2015, at 5:36 AM, Andrea Giammarchi <andrea.giammarchi at gmail.com>
> wrote:
>
> That's similar to the Labeler proposed by Mark, except it needs to search
> for the thing twice (wm.has + wm.get instead of just wm.get which would be
>  just fine as check if you count from 1 instead of 0 ;-) )
>
> Although I need to understand if you have a wm why wouldn't you just use
> that instead of a Symbol ... so the Labeler seems again a more appropriate
> pattern for this problem.
>
> Just my thoughts
>
> On Wed, Sep 9, 2015 at 10:51 AM, Michał Wadas <michalwadas at gmail.com>
> wrote:
>
>> Following solution will work:
>>
>> (function(){
>> const wm = new WeakMap();
>> Symbol.identity = Symbol( 'Symbol.identity' );
>> let i = 0;
>> Object.defineProperty(
>>   Object.prototype,
>>   Symbol.identity,
>>   {
>>     get: function () {
>>       if (wm.has(this)) return wm.get(this);
>>       wm.set(this, Symbol(i++));
>>       return wm.get(this);
>>     }
>>   }
>> );
>> })()
>>
>>
>> 2015-09-08 23:29 GMT+02:00 Andrea Giammarchi <andrea.giammarchi at gmail.com
>> >:
>>
>>> as side note, that's just a lazy assignment that doesn't need two
>>> symbols and a constant get invoke ...
>>>
>>> ```js
>>> Symbol.identity = Symbol( 'Symbol.identity' );
>>> var OBJECT_ID = 0;
>>> Object.defineProperty(
>>>   Object.prototype,
>>>   Symbol.identity,
>>>   {
>>>     get: function () {
>>>       // first time this is invoked ... and no more ...
>>>       Object.defineProperty(this, Symbol.identity, {value: ++OBJECT_ID});
>>>       // from now own, direct property access \m/
>>>       return this[Symbol.identity];
>>>     }
>>>   }
>>> );
>>> ```
>>>
>>> Regards
>>>
>>> On Tue, Sep 8, 2015 at 9:57 PM, Michael McGlothlin <
>>> mike.mcglothlin at gmail.com> wrote:
>>>
>>>> I try to keep it pretty simple. It's not fancy but the times you want
>>>> fast and dirty information like this are the same times you don't want to
>>>> have to define it manually.
>>>>
>>>>  Symbol.identity = Symbol( 'Symbol.identity' );
>>>>  const identity = Symbol( 'identity' );
>>>>  var OBJECT_ID = 0;
>>>>  Object.defineProperty( Object.prototype, Symbol.identity, {
>>>>   get: () => {
>>>>    if ( !Object.hasOwnProperty.call( this, identity ) ) {
>>>>     this[ identity ] = ++OBJECT_ID;
>>>>    }
>>>>    return this[ identity ];
>>>>   }
>>>>  } );
>>>>
>>>> On Tue, Sep 8, 2015 at 1:44 PM, Mark S. Miller <erights at google.com>
>>>> wrote:
>>>>
>>>>> See Labeler at
>>>>> http://wiki.ecmascript.org/doku.php?id=harmony:weak_maps#unique_labeler
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Sep 8, 2015 at 11:16 AM, joe <joeedh at gmail.com> wrote:
>>>>>
>>>>>> Didn't send to list, something is wrong with my reply all. Sorry
>>>>>> about that. Stupid mobile gmail.
>>>>>> ---------- Forwarded message ----------
>>>>>> From: "joe" <joeedh at gmail.com>
>>>>>> Date: Sep 8, 2015 11:15 AM
>>>>>> Subject: Re: Object id, hash, etc?
>>>>>> To: "Garrett Smith" <dhtmlkitchen at gmail.com>
>>>>>> Cc:
>>>>>>
>>>>>> I agree with this request. This is the logical complement to valueof,
>>>>>> I think. And yes, for most ID use cases this isn't a good fit, but we're
>>>>>> not talking about the general case, just the cases where a python style
>>>>>> id() function *is* appropriate.
>>>>>>
>>>>>> Joe
>>>>>> On Sep 8, 2015 9:08 AM, "Garrett Smith" <dhtmlkitchen at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> On 9/8/15, Michael McGlothlin <mike.mcglothlin at gmail.com> wrote:
>>>>>>> > Is there a reason not to provide an object id and hash value as
>>>>>>> other
>>>>>>> > languages often do? I find myself defining an identity symbol on
>>>>>>> objects
>>>>>>> > with a value from a simple global counter. It makes it easier to
>>>>>>> debug if I
>>>>>>> > can just look at a log and see what objects and functions were
>>>>>>> active.
>>>>>>> >
>>>>>>> > Likewise a hash value would simplify a lot of comparisons and make
>>>>>>> it easier
>>>>>>> > to debug.
>>>>>>> >
>>>>>>> > I especially find the ID useful when working with bound functions
>>>>>>> as they
>>>>>>> > can be difficult to tell apart. I like to change toString() to
>>>>>>> provide the
>>>>>>> > ID followed by the code (flattened to one line).
>>>>>>> >
>>>>>>> >
>>>>>>>
>>>>>>> NFE's are safe to use where IE8 support isn't needed*.
>>>>>>> (function aa(){}).name; // "aa"
>>>>>>>
>>>>>>> As for using Object IDs and Object Pooling, lexically-scoped values
>>>>>>> have benefits over global ID generators (as your counter). The values
>>>>>>> can be passed in as a parameter to the Factory (useful with Private
>>>>>>> Proxy). There other benefits to this pattern regarding memory
>>>>>>> management and application design. Contact me if you'd like to learn
>>>>>>> more.
>>>>>>>
>>>>>>> * https://kangax.github.io/nfe/
>>>>>>> --
>>>>>>> Garrett
>>>>>>> @xkit
>>>>>>> ChordCycles.wordpress.com
>>>>>>> garretts.github.io
>>>>>>> personx.tumblr.com
>>>>>>> _______________________________________________
>>>>>>> es-discuss mailing list
>>>>>>> es-discuss at mozilla.org
>>>>>>> https://mail.mozilla.org/listinfo/es-discuss
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> es-discuss mailing list
>>>>>> es-discuss at mozilla.org
>>>>>> https://mail.mozilla.org/listinfo/es-discuss
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>     Cheers,
>>>>>     --MarkM
>>>>>
>>>>> _______________________________________________
>>>>> es-discuss mailing list
>>>>> es-discuss at mozilla.org
>>>>> https://mail.mozilla.org/listinfo/es-discuss
>>>>>
>>>>>
>>>>
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>
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