On Mon, Jan 16, 2012 at 12:56 PM, Mark S. Miller <[email protected]> wrote:
> I like the idea of the two argument get as proposed by David. (In fact, I > like it so much that I thought I'd already specified it that way ;).) > David, I'm glad to see you got it right in your suggestion at < > http://wiki.ecmascript.org/doku.php?id=harmony:weak_maps#alternate_spec_based_on_ff6.0a1 > >. > > Axel, I do not like your elaboration because it turns a query operation > into a possibly occasionally side-effecting operation. As it is now, I can > give someone a read-only view of a WeakMap wm my simply giving them > ... *by* simply giving them... > > { get: wm.get.bind(wm), has: wm.has.bind(wm) } > > > On Mon, Jan 16, 2012 at 12:26 PM, Axel Rauschmayer <[email protected]>wrote: > >> One probably should separate two concerns: providing a default value vs. >> adding missing values to the collection. >> >> One possible signature: >> >> function get(key, default = undefined, addIfMissing = false) >> >> The above would also allow you to store `undefined` and detect missing >> values, by using a special value (e.g. named NO_VALUE) as the default. >> >> On Jan 16, 2012, at 21:09 , David Bruant wrote: >> >> Hi, >> >> I recently wrote some code using WeakMaps and the following pattern >> keeps coming over and over: >> ----- >> var v = wm.get(o); >> if(v === undefined){ >> v = someValue; >> order.set(o, v); >> } >> >> // now, wn has a value for o (either it already did or it's been added) >> // v === wm.get(o) >> // play with v >> ----- >> >> The "v === undefined" is fine in my case, because I know I never store >> "undefined" as a value. >> >> I thought that maybe the semantics of WeakMap#get could be changed >> whenever the key is not used to set the value and return it. >> My pattern would be reduced to: >> ----- >> var v = wm.get(o, someValue); >> // now, wn has a value for o (either it already did or it's been added) >> // v === wm.get(o) >> // play with v >> ----- >> >> Thinking more about the current semantics, I thought that what is >> currently done could be achieved a bit differently: >> ----- >> var v = wm.get(o, def); >> // almost equivalent to: >> var v = wm.get(o) || def; >> ----- >> There is a difference when the vaue stored in the weak map is a falsy >> value. >> >> My personal experience is to store mostly objects (so truthy) as weak >> map values, so I wouldn't be affected. Has anyone else experience in >> storing falsy values? >> >> David >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> >> >> -- >> Dr. Axel Rauschmayer >> [email protected] >> >> home: rauschma.de >> twitter: twitter.com/rauschma >> blog: 2ality.com >> >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> >> > > > -- > Cheers, > --MarkM > -- Cheers, --MarkM
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