On Mon, Apr 7, 2008 at 10:45 AM, Neil Mix <[EMAIL PROTECTED]> wrote: > > On Apr 7, 2008, at 10:37 AM, Steven Johnson wrote: > > Dynamic classes also incur nontrivial overhead in memory use and > > runtime > > performance. IMHO we'd want a fairly compelling argument for making > > all > > classes dynamic by default. > > It would probably put an end to the acrimony about ES4 being too > different from ES3; I'm hesitant to speak for the views of others, but > I suspect this change would make the language a lot more palatable for > many currently opposed to it. In that light, "compelling" is going to > be a highly subjective measurement.
Speaking as one of the more vocal skeptics, this change would make ES4 less palatable for me. ES3.1 and ES4 are together moving in a good direction by making the degree of permissiveness controllable on a per-property and per-object basis. Subjectively, as someone interested in robustness, integrity, and security, ES3 made a huge mistake in having all these be as permissive as possible. Both ES3.1 and ES4, in order to be reasonably compatible with ES3+R, must continue to have the ES3 constructs default to overly permissive. For ES3.1 the best we can do is provide explicit operations (such as __defineProperty__) for overriding these defaults. To my mind, the main virtue of introducing a class syntax to an ES is an opportunity to get these defaults right this time. One principle of security engineering is "deny by default is better than allow by default"; which is closely related to "whitelisting is better than blacklisting". For ES3.1, we're stuck with allow-by-default. If the ES4 class syntax were to get this wrong as well, I'd be even more puzzled about what its purpose is. Accordingly, my preference is for classes to default to non-dynamic and non-subclassable. For methods to default to non-overridable and non-enumerable. And for properties/members to default to non-settable and non-enumerable. Whatever these defaults are, it's an orthogonal question whether classes need to be a primitive construct, or whether they should be just sugar for a less-permissive-by-default usage of the class-like abstraction pattern of ES3.1. -- Cheers, --MarkM _______________________________________________ Es4-discuss mailing list Es4-discuss@mozilla.org https://mail.mozilla.org/listinfo/es4-discuss
