726298 - Expose Map and Set size

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jason Orendorff [:jorendorff]]

There is currently no way to ask how many entries are in a Map or Set.

TC39 apparently did not reach a consensus at the last meeting as to what this method or accessor should be called. I don't have an opinion. I'm going with size().

Comment 1

[Jason Orendorff [:jorendorff]]

Attachment: v1

Comment 2

[Luke Wagner [:luke]]

Comment on attachment 596323 [details] [diff] [review]
v1

Review of attachment 596323 [details] [diff] [review]:
-----------------------------------------------------------------

Sorry for the delay.

::: js/src/builtin/MapObject.cpp
@@ +246,5 @@
>  JSBool
> +MapObject::size(JSContext *cx, uintN argc, Value *vp)
> +{
> +    THIS_MAP(get, cx, argc, vp, args, map);
> +    args.rval().setNumber(double(map.count()));

How about a

  JS_STATIC_ASSERT(sizeof map.count() <= sizeof uint32_t);

here and in SetObject::size?

Comment 3

[Jason Orendorff [:jorendorff]]

Hmm. Currently we have:

   uint32_t js::detail::HashTable<>::count() const;
   size_t js::HashMap<>::count() const { return impl.count(); }
   size_t js::HashSet<>::count() const { return impl.count(); }

So, do you mean I should change the latter two to return uint32_t? If so, then I can add the static assertions you mention and remove the 'double()' part.

Comment 4

[Luke Wagner [:luke]]

Oops, didn't even realize that; that's a bug; HashTable::count returns a uint32_t.  Yes, changing them sounds good.

Comment 5

[Marco Bonardo [:mak] (Away Apr 25 - May 5)]

https://hg.mozilla.org/mozilla-central/rev/3f51e7052b7d

Comment 6

[Marco Bonardo [:mak] (Away Apr 25 - May 5)]

https://hg.mozilla.org/mozilla-central/rev/2d534a06e561

Comment 7

[Tom S [:evilpie]]

Added the method description and added it to the example code.
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Map an Set