Separating a Hash type from Object

[Graydon Hoare]

Jason Orendorff wrote:

> OK, it strikes me as a little weird, now, to use intrinsic::=== and
> intrinsic::hashcode() here.
> 
> Java, Python, and Ruby let individual *classes* (rather than individual
> hash tables) override hash() and equals().  I think this supports
> generic code better.

Not all objects in ES4 are of an interesting class, or implement an 
interesting interface. Think structural types: the nearest class of the 
type "{a:int}" is "Object".

Still, it's pretty easy to have both:

function defaultHash.<K>(k:K) : uint {
   switch type (k) {
     case (h:Hashable) {
       return h.hash();
     }
     default {
       intrinsic::hashcode(k);
     }
   }
}

function defaultEq.<K>(a:K, b:K) : bool {
   switch type (k) {
     case (h:Equality) {
       return a.equals(b);
     }
     default {
       return a === b;
     }
   }
}

class Dict.<K,V> {
   function Dict(hash=defaultHash.<K>, eq=defaultEq.<K>)
   {
    ...
   }
...
}

-graydon