Does private(expr) create a private storage block?

Herby Vojčík herby at
Thu Jan 19 13:00:48 PST 2012


Mark S. Miller wrote:
> ... I don't have strong feelings about this for non-const
> classes. For const classes, I think privates should always be declared
> in the constructor. I would like to be able to always allocate instances
> of const classes of fixed "shape", i.e., non-configurable /
> non-extensible, so that users don't have to worry about whether they've
> enabled the resulting optimizations or whether they have uncaught
> spelling errors.

It is written in class proposal:

- An efficient implementation. The private state should be allocated 
with the instance as part of a single allocation, and with no undue 
burden on the garbage collector.
- The ability to have private mutable state on publicly frozen objects.

Now it is the question, what does it say about "fixed shape". Does 
"fixed shape" mean no private can be added / deleted, but private 
properties themselves can be mutated? Or is it the weaker "the private 
space must be created and is not removable (in frozen object), but it is 
itself extensible and private properties are configurable and writable"?

> For consistency, perhaps we should make similar requirements for
> privates of non-const classes, but this isn't clear. If you have some
> arguments one way or another, please post. Thanks.

I have more thoughts on this, even the proposal how to make it work 
dynamically for non-const classes and "fixed" in const classes, but the 
answer to previous question seems important.

I presume the answer is "the latter", since "with no undue burden on the 
garbage collector" could be read as "if possible, blended in single 
object". But I would like to hear from you.

> On Mon, Jan 9, 2012 at 8:33 AM, Herby Vojčík <herby at
> <mailto:herby at>> wrote:
>     Hello,
>     the current class proposal (as I read it) specifies that the private
>     block is created by first 'private foo[ = "bar"];' in the
>     constructor. The question is, what is constructor does not contain
>     any private declarations, but uses private, like this:
>     class Coutner {
>       constructor () {
>        this.reset();
>       }
>       increment () {
>        private(this).c++;
>       }
>       reset () {
>        private(this).c = 0;
>       }
>       get count () {
>        return private(this).c;
>       }
>     }
>     The reset method is part of the API. Conveniently, it resets the
>     state of the object to the initial state, so constructor is calling it.
>     The question is: does private(this) create the private storage block
>     in this case?
>     Herby
> --
>      Cheers,
>      --MarkM

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