On Sep 26, 2009, at 6:08 PM, Maciej Stachowiak wrote:
- Note: I think catchall deleters are used only by Web Storage and
not by other new or legacy interfaces.
Seems like a strong reason to change to the proposed API to
eliminate the need for
a new ES language extension.
I previously argued for removing the need for catchall deleters from
the Web Storage API (since nothing else requires , but other browser
vendors (including Mozilla) were happy with it,
"(including Mozilla)" and "happy with it" leave out some nuance:
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2008-May/014856.html
Robert O'Callahan here wrote "If overloading "delete" is too quirky or
too hard to implement, then it seems none of the other shorthands
should be allowed either." His message adverted to the better course
of methodical access instead of property access to Web Storage keyed
values.
Alas Rob finally gave up at:
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2008-May/014868.html
I think the Web Storage key/value reflection as properties is a
mistake. Sorry I wasn't reviewing it in time to say so. But it was
obviously not a situation everyone was "happy" with, even ignoring the
issue of delete.
and I think now everyone (including I believe Microsoft) has
implemented the spec behavior. See prior discussion thread here: <http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2008-May/014851.html
>. At this point, since we have multiple deployed implementations
of Web Storage, we'd have to investigate whether it's safe to remove
this behavior without breaking content.
We could try to remove it -- or (what is more likely to go down
easily) we could add methods and let the property reflections wither,
and vow to avoid repeating this mistake.
2) Ability to support being called (via [[Call]]) without being a
Function.
Not an issue with the core ES5 semantics. Most ES3/5 section 15
functions have this
characteristic. As long as such WebIDL objects are defined
similarly to the "built-in"
function they too can have this characteristic. It may well be
useful to introduce a
mechanism defining such "pure" functions in the language but it
probably isn't necessary
to proceed with the WebIDL binding. The important thing to try to
avoid is specify
a custom [[Call]]
I tend to agree that this behavior (and the next 3) are not
philosophically problematic, even though they cannot today be
implemented in pure ECMAScript.
What does typeof say for such a callable object?
In what sense are any DOM methods required to be not Functions (native
function objects) in the specs? In Netscape of old and Mozilla
browsers since 1998, DOM methods are native function objects.
This seems winning since developers want not only sane typeof,
but .apply/call/bind.
We've talked on es-discuss about "pure" functions (ones without
[[Construct]] and .prototype) before:
https://mail.mozilla.org/pipermail/es5-discuss/2009-July/002920.html
in case you missed the thread. Agreed it's not a big deal. We have a
bugzilla.mozilla.org bug on file to fix our built-in functions (Date
methods, etc.) to lose [[Construct]] and .prototype. I'm not sure of
v8's plans.
First-class syntax for defining such non-constructor functions is
elusive. ;-)
3) Ability to support being invoked a constructor (via
[[Construct]])
without being a Function.
Essentially same as 2 although the standard [[Construct]] requires
a [[Call]] so this
may need some more thought.
Is there anything specified via WebIDL that must be a constructor but
not a callable?
Ye olde Image and Option, at least, act like most built-in
constructors by constructing when called, at least in Gecko and I
think IE -- but not in WebKit (I just tested).
4) Ability to support instanceof checking (via [[HasInstance]])
without being a constructor (so myElement instanceof HTMLElement
works).
Possibly the specification of the instanceof operator needs to be
made extensible
Definitely.
5) Ability to have [[Construct]] do something different than
[[Call]]
instead of treating it as a [[Call]] with a freshly allocated Object
passed as "this".
Similar to 4 regarding extensibility. At least one recent
"harmony" strawman proposal is
moving in a direction that may be relevent to 4 and 5.
See http://wiki.ecmascript.org/doku.php?id=strawman:obj_initialiser_constructors
Interesting.
As an aside, the strawman for 'constructor' makes at least Mark Miller
and me want to unify 'class' and 'constructor' -- we don't want both,
and Harmony needs something already called class for several reasons,
one of them to model built-ins in ES1-5.
This may provide a way to implement some of these behaviors in pure
ECMAScript. The current proposal does allow [[Construct]] without
[[Call]], but not [[Call]] and [[Construct]] that both exist but
with different behavior.
Date needs the latter.
/be
