Le 26/05/2012 17:55, Allen Wirfs-Brock a écrit :
On May 26, 2012, at 2:37 AM, David Bruant wrote:
The use case of subclassing native constructors (just to clarify I'm
only talking about Array, Date, WeakMap, etc. Not DOM constructors)
is legitimate and has been raised and detailed in length [1] (the
initial message does not point that out, but the rest of the thread
does). Being able to *securely* do that is still a use case.
The proto operator was a solution to it but it's out. __proto__ is
out because secure JS code first instruction will be to delete it on
go on as if it never existed. Extracting just a __proto__ setter is
not an option according to what you're saying below. What is there
left for the subclassing use case? So far, I don't see anything.
The aforementioned thread raised 2 interesting alternatives to
__proto__ [2] [3] for the subclassing use case. Could it be
considered to standardize any of these functions (or something else
as long as it solves the use case)?
Unlike grawlix, this function will be polyfillable with __proto__
where it's available. In platform with a native support for this
function, it will be possible to both use this function (solving the
use case) and delete __proto__ (doing it safely).
Does it sounds like a good alternative?
Because max-min classes are inching towards consensus, I suggest the
that appropriate way to subclass the built-in constructors will be via
|class extends|. eg
class MyArray extends Array {
someMyArrayProtoMethod () {...}
constructor (tag) {
super();
this.tag=tag
}
}
If that's the case, then that's perfect!
It suffers from the same issue than <| which is that it's syntax-based,
so minimum cost is an ES6->ES5 compiler
I'm quite confident this can be made to work in a backwards compatible
manner. I will write a strawman explaining the details.
Also I believe Date and many of the other built-ins can be respecified
in a manner that enables them to be subclassed using traditional ad
hoc techniques. For example, the only real "magic" in Date instance
is its [[PrimitiveValue]] internal property. Date can be made
subclassables by replacing [[PrimitiveValue]] by a regular property
with a private name.
Finally, note that in the Internationalization spec. [1] we have
tried to avoid the subclassing problem from the start. Even though the
constructor defined in that spec. create instances that make extensive
use of [[internal properties]] they have been defined in a manner that
enables even ad hoc "subclassing". All it takes is an actual or
equivalent super call. EG:
Intl.Collator.call(collatorSubclassInstance). I favor adopting the
pattern used in [1] for all new built-in constructors.
Allen
[1]:
http://wiki.ecmascript.org/doku.php?id=globalization:specification_drafts
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