An there is nothing stopping someone from defining their own map class (possibly by subclassing Map) that has its own hashing and comparison policies. JS implementations + ES6 functionality are good enough that we don't have to wait for such things to be built-in.
Allen On Apr 6, 2014, at 3:51 PM, Rick Waldron wrote: > > > On Sunday, April 6, 2014, K. Gadd <[email protected]> wrote: > I guess the analog for this in traditional JS 'Object' instances is > that when you use the [] operator, i.e. obj[valueObject], it actually > does obj[valueObject.toString()], so you can control the 'hashing > function' in a sense by overriding toString. It seems natural to want > something equivalent here, preferably not based on strings... (though > I don't know how people feel about exposing hash internals and saying > 'your hash key needs to be an integer') > > Map would certainly be far more useful if it had support for > customizable hashing, > > Existing hash code related work: > > http://wiki.ecmascript.org/doku.php?id=strawman:encapsulated_hashcodes > > http://wiki.ecmascript.org/doku.php?id=proposals:hashcodes > > There was also discussion when parameterization of the Map and Set comparator > was first added, but custom comparator functions were deferred until some > time in which object hash codes are available: > https://github.com/rwaldron/tc39-notes/blob/master/es6/2013-01/jan-29.md#43-parameterize-the-equivalence-operator-for-mapset > > Rick > > > > otherwise it's just a slightly faster > replacement for Objects with cleaner semantics. Maybe making it > possible to get the same value back using two different keys that > don't compare the same with === is against the purposes here, though. > > On Sat, Apr 5, 2014 at 10:21 PM, Benjamin (Inglor) Gruenbaum > <[email protected]> wrote: > > I'd like to raise an issue with ES7 value objects with maps raised here: > > > > http://esdiscuss.org/topic/maps-with-object-keys > > > > To save you all time, let me sum things up: > > > > ES6 maps don't solve a particular (but common) issue for me - using compound > > objects as keys. I do a lot of statistical analysis and I need keys to be > > compound tuples or other values. This is currently not possible with ES6 > > since map key equality is checked with `===` so it is always reference > > equality > > > > ES7 introduces value objects - which are really cool anyway. This allows for > > compound keys.which partially solves my issue because value keys are > > compared structurally with `===`. > > > > However, it does not let me index on partial information (described in my > > last commend on that issues). Since it is impossible to override `===` in > > value objects from what I understand - It would be impossible for me to use > > partial objects as keys. > > > > To illustrate, if for example I have a lot of 10 dim vectors, and I want to > > index them as keys based on their first two dimensions - it is impossible at > > the moment and I have to project them into their 2d counterparts which have > > no further use for me. > > > > Is this somehow addressed? I'm unsure where to look for answers. It seems > > natural to me to allow specifying a hashing function in the `Map` > > constructor (rather than on every type) to solve this particular (but again, > > rather common in code that does crunching) problem. > > > > Thanks, > > Benjamin > > > > _______________________________________________ > > es-discuss mailing list > > [email protected] > > https://mail.mozilla.org/listinfo/es-discuss > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss
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