I’m not sure that there is much one can do to protect programmers from
themselves, given that writing good hash functions is hard. One could provide a
test suite.
Random thoughts:
- Enforce that both equality and hash function are specified. A common Java
problem.
- Provide a hash function to complement Object.is() – Brandon suggested
Object.hash().
- Most common case: two objects are considered equal if (e.g.) two of their
properties are equal. How can we help programmers here? Combining equals seems
easy, combining hashes harder:
function hashPerson(p) {
return Object.combineHash(Object.hash(p.last), Object.hash(p.first));
// Alternative: Object.hash(p.last, p.first)
}
function equalsPerson(p1, p2) {
return Object.is(p1.last, p2.last) && Object.is(p1.first, p2.first)
}
- Internationalization mainly seems to matter for sorting, so it’s probably not
an issue here.
On Dec 27, 2011, at 19:20 , Mark S. Miller wrote:
> Hi Axel, yes, I would like to extend their constructor in this way. However,
> I'm not sure how to spec it -- help appreciated. The problem is that the
> comparator needs to provide both an equivalence operation and a corresponding
> hash operation. When these agree, all is well. What should we specify happens
> when passing in a misbehaving comparator? The dilemma is that
> 1) detecting misbehavior is expensive,
> 2) having a deterministic collection misbehavior in the face of comparator
> misbehavior seems hard, and
> 3) we'd like to avoid yet more under-specification. The similar
> under-specification of Array.prototype.sort is already bad enough.
>
> On Tue, Dec 27, 2011 at 7:22 AM, Axel Rauschmayer <a...@rauschma.de> wrote:
> http://wiki.ecmascript.org/doku.php?id=harmony:simple_maps_and_sets
>
> Currently, using Object.is() is hard-coded. But one could allow a comparator
> function being handed in (with Object.is being the default).
--
Dr. Axel Rauschmayer
a...@rauschma.de
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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