Erik Corry wrote:
Hi
This proposal offers a way to get around some of the strange semantics
of '=', specifically the way read-only properties and setters on
objects in the prototype chain can restrict what you can do on the
receiver of an assignment.
This is "strange" only insofar as you can't say what you mean if you
want to override. There's no law of nature requiring = to override, though.
Assigning != defining in ES5, even in reality in fixed implementations
of ES3, and in truth going back to the first JS implementation:
proto-setters (internal, hidden) are invoked by assignment, readonly
proto-props prevent = being used to override on a delegating object
(silent failure, of course, due to lack of try/catch).
What I'm getting at: is assignment != defining strange, or is the lack
of expressiveness that left JS with = but not := strange, or is = not
defining strange? I didn't want to assume the last was what you meant,
since it is not obvious and not the only possible strangeness or asymmetry.
However it has some strangeness itself:
* There is little point in having read-only properties if the common
way to do assignment is :=. := will just walk all over a read-only
property.
No, readonly properties must be {writable: false, configurable: false}
to have integrity, and := cannot redefine a non-configurable property.
* Copying private members from one object to another violates the
encapsulation pretty badly. You would hope that using private names
allowed you to easily reason about which objects have which
properties, just by looking at the limited number of places a private
name is used. But with this any code in the system that has two
instances of a class can splat object a's private properties with
those from object b. It's rather like a replay attack in crypto.
Yes, this is an open issue in my view. If one uses a private name to
brand an object, attackers who have access to such an object can use :=
to forge trojan objects.
* I don't understand the super stuff.
Allen should field this one.
/be
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