Closed Bug 551529 Opened 11 years ago Closed 10 years ago

Remove __count__

Categories

(Core :: JavaScript Engine, defect)

defect
Not set
minor

Tracking

()

RESOLVED FIXED
mozilla1.9.3a4

People

(Reporter: Waldo, Assigned: Waldo)

References

Details

(Keywords: dev-doc-complete, Whiteboard: fixed-in-tracemonkey)

Attachments

(1 file)

The appeal, at least as I understood it, is that it allows you to quickly and efficiently determine the number of own properties of an object, without some sort of ungainly loop structure.  That said, it seems it isn't actually "efficient", at least in the sense of not being O(n) in the number of properties on the object, for normal JS objects, because it uses the mechanism of initializing an enumerator to get the property count -- but initializing an enumerator iterates through all properties!  So either way you still have this linear-time loop; the question is whether it's hidden behind an engine-specific per-object magical property, hidden through some less magical mechanism, or not provided at all (left to the developer to write himself -- slower than the near-max-speed native-code loop in obj_enumerate, but not asymptotically so).

I favor removing __count__ entirely.  If experience from such a change demonstrates use such that we need to support it, we can make it a getter directly on Object.prototype, which would still give people the tool without giving it to them in a way that requires special treatment in the engine.
Just remove it. No turd-polishing now that we have ES5 and its (costly but who cares) ways to count properties.

/be
Summary: Make __count__ non-special, either by removing it or by making it a getter on Object.prototype → Remove __count__
Attached patch KILL THEMSplinter Review
Attachment #431717 - Flags: review?(shaver)
Comment on attachment 431717 [details] [diff] [review]
KILL THEM

Aw yeah.
Attachment #431717 - Flags: review?(shaver) → review+
http://hg.mozilla.org/tracemonkey/rev/44f70f0e8bb2
Status: NEW → ASSIGNED
Whiteboard: fixed-in-tracemonkey
Target Milestone: --- → mozilla1.9.3a4
Great.

__parent__ next, right?

/be
Sure, will file another bug for that.
You should probably fix http://mxr.mozilla.org/comm-central/source/suite/browser/test/browser/browser_pluginnotification.js too, to avoid comm-central bustage when this lands on mozilla-central.
I'm fixing the c-c bit once a pul -u completes.

I have a blog post queued up on this topic, just waiting for a TM->m-c merge and a nightly cycle so there's something concrete to point developers toward...
Updated this on MDC:

https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Object/prototype#section_3

but pretty sure there's more -- crussell on IRC fixed up the property-inheritance template as well.  Other places -- at least the traditional "What's new" document -- still need fixing.
http://hg.mozilla.org/mozilla-central/rev/44f70f0e8bb2
Status: ASSIGNED → RESOLVED
Closed: 10 years ago
Resolution: --- → FIXED
Depends on: 620344
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