Minimalist Classes

David Bruant bruant.d at
Wed Nov 2 11:17:41 PDT 2011

Le 02/11/2011 19:00, Brendan Eich a écrit :
> On Nov 2, 2011, at 10:35 AM, David Bruant wrote:
>> Le 02/11/2011 18:09, Brendan Eich a écrit :
>>> On Nov 2, 2011, at 4:10 AM, David Bruant wrote:
>>>> Another topic:
>>>> -----
>>>> class Monster {
>>>>  private name, health;
>>>>  sameName(other) {
>>>>    return @name === other at name;
>>>>  }
>>>> }
>>>> -----
>>>> I am under this impression that you are accessing the private property ("other at name") of an instance which isn't you (other !== this) and I'm not sure it's a good idea.
>>> Private names do not leak via reflection, not even via proxies. So what's the problem?
>> My problem is that private names are per-class instead of per-instance.
> See my reply to Kam. We're not sugaring instance-private ivars. I am proposing something we agreed to in Nov. 2008: sugaring class-private ivars.
Ok, that's what I was missing. What were the rationale? use cases?

> You can make instance-private ivars yourself in the constructor using Name.create, and go to town. Knock yourself out! (I mean that in a good way, at least from where I sit :-P).
Hmm... Are you sure you can implement instance-private variables with no
Within the constructor, you can call Name.create, but where do you store
the name? If in a constructor local variable, it's not usable anywhere
else which is useless. If in a private class variable... well... that's
not an instance-private name anymore.
The private class variable could be a WeakMap indexed on instances, but
it means that any instance with a reference to another instance can
access the "private" value of the latter. That's not private.
Am I missing something?
If I can implement them myself, I promise, i'll knock myself out to town
(damn, it's hard being a non-native English speaker. So many expressions
I'm never sure I fully understand)

>>>> Is "other" a monster? (how do you "recognize" a monster from any other object?).
>>> You could do ad-hoc type or shape tests. For the example, and even in most cases in general, there's no need. Duck typing works with private names too.
>> Who is "you" in your case? My "you" was "runtime". I think runtime
>> shouldn't do heuristic-tests like comparing shapes.
> We don't have types. I have no idea what you are proposing, but my point stands: there's no need to recognize another Monster and no capability leak. The code works as much JS today does with public property names.
Ok. I thought @health refered to a per-instance name. Now I know it's a
per-class name, other at health makes sense.


More information about the es-discuss mailing list