False alarm. I have finally (just) received the e-mail. David
Le 11/05/2011 21:44, Oliver Hunt a écrit : > On May 11, 2011, at 12:38 PM, David Bruant wrote: > >> Le 11/05/2011 20:38, felix a écrit : >>> On Wed, May 11, 2011 at 11:16, David Bruant <[email protected]> wrote: >>>> A memoizer could be written to improve f time performance (by the cost of >>>> memory, of course). >>>> ---- >>>> function memoizer(f){ >>>> var cache = WeakMap(); >>>> return function(o){ >>>> var res; >>>> if(WeakMap.has(o)) >>>> return cache.get(o); >>>> res = f.apply(this, o); >>>> >>>> cache.set(o, res); >>>> }; >>>> } >>>> ---- >>> I'm not sure I understand your code. >>> >>> it's not clear to me why you need .has at all, since you can check the >>> return value of .get instead. in the case where 'undefined' is a >>> valid value that you would want to memoize, you can store a unique >>> object to represent 'undefined'. >> The ambiguity of "get" returning "undefined" when the key is actually >> undefined or when it is defined but its value is "undefined" already >> happened with objects. The solution to that was the "in" operator (or >> Object.prototype.hasOwnProperty depending on cases). I'm just asking an >> equivalent for weak maps. I agree its not necessary as proved in >> harmony:weak_maps#explicit_soft_own_fields . However, a native >> implementation would be a good addition. > So you want to do > if (map.has(bar)) > wiffle = map.get(bar) > > or some such? > > The problem here is that you can't guarantee that GC won't happen between > those two calls, and therefore you could still end up getting undefined in > response to the get. > > GC is (from the language's perspective) non-deterministic, so any non-atomic > operation with a weak map leads to "non-sensical" behaviour. > > --Oliver > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
