Le 06/06/2011 18:30, Mark S. Miller a écrit : > > > On Mon, Jun 6, 2011 at 2:46 PM, David Bruant <david.bru...@labri.fr > <mailto:david.bru...@labri.fr>> wrote: > > Le 06/06/2011 17:41, Mike Samuel a écrit : > > 2011/6/6 David Bruant <david.bru...@labri.fr > <mailto:david.bru...@labri.fr>>: > >> The consequence of this second point is wondering whether it's > a good idea > >> to standardize WeakMap (instead of Map) at all. > > Besides a lack of out-of-memory errors and performance, a program > > using an object key map that doesn't use ephemeron pairs shouldn't > > behave differently than one that does. But developers need to have > > some idea of memory performance when choosing an appropriate > > collection. If you're documenting, I would document the behavior > > around GC upon which devs can rely. > Not only there is a memory performance difference, but also a key > enumerability difference. With WeakMaps, keys cannot be enumerated > in a > determinist manner while they can with Map. > > > > This enumerability is crucial to the difference in how conservative an > approximation to "will not be used" needs to be to be safe. If we got > rid of WeakMap and only had enumerable Map, the GC would need to > determine that a given map would never be enumerated in order to gc it > as aggressively. Put another way, resource issues aside, WeakMap's > contract is merely the non-enumerable subset of Map's contract. The GC > knows that a WeakMap won't be enumerated because it can't be. So maybe that the harmony:simple_maps_and_sets proposal should do the "todo" and add the iteration (or an enumeration) method. Otherwise, the Map proposal has no more value than the WeakMap proposal ;-)
David
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