On "private per-object state"

Herby Vojčík herby at mailbox.sk
Sat Dec 17 05:56:19 PST 2011


Hello,

I see some discrepancies between dynamic slot-based ES versus concept of 
"private per-object state".

The main problem seems to be that I can do this:

  (function() { return private(this).secret; }).call(obj);

In that case, I can read (and also write) object's private property at will. 
But how is it ten private?

The problem I see is in notion of "per-object" - if you want the property be 
private for any method of an object, but not accessible "from outside", you 
can make anything method of an object and access it. It may be the case of 
http://c2.com/cgi/wiki?BlubParadox though I hope it is not, but it seems to 
me the only conceivable method of "private state" is "private per-scope 
state", and I mean scope more broadly - not a function scope, but a "bunch 
of methods"-scope. Because, it seems to me, first we should ask the question 
"why do we want private?" and the answer seems to be "to have state that can 
only be accessed and modified by narrow subset of code" and I strongly 
believe that this "narrow subset of code" is always closed, not open, that 
is, it is a bunch of methods (and constructors, and static methods) that 
realize certain functionality where they need to share some state, but this 
state is _not_to_be_disclosed_ to anyone else (even other methods of the 
same class added later, or subclasses, or superclasses, or the ad-hoc method 
from beginning of the post).

That leads me to the conclusion (and here it may be I fell victim to the 
Blub syndrome) that only natural "private" is the (lexical; but lexical only 
because it is easy way of grouping methods that will share access to it, not 
lexical per se) scope private; in the present state of class proposal, the 
private that can be accessed by all methods in class definition block, but 
no other.

Please clear my mistakes, if you find any :-)

I'd like to see real "per-object private" use case for such dynamic language 
as ECMAScript is. Thank you,

Herby 



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