typed objects and value types

[Dmitry Lomov]

On Wed, Apr 2, 2014 at 8:26 PM, Mark S. Miller <erights at google.com> wrote:

>
>
> We could specify that WeakMaps can use typed objects as keys. The current
> discussion in your article confuses semantics with implementation when it
> speaks of typed objects comparing structurally. Typed objects have
> identity, characterized by the four-tuple you explain. Just as all the bits
> of a thin pointer are significant when comparing two thin pointers to see
> if they point at the same semantic object identity, so are all the bits in
> your fat pointer significant. Don't get confused by the bits in the pointer
> to the fat pointer, when the fat pointer happens to be boxed.
>

It is unclear to me how WeakMaps can ever use typed objects as keys, since
typed objects do not have their unique identity. Or rather, the only
possible semantics I see is "hold to the value forever". So for example:

   w = new WeakMap();
   w[Point(buffer, 0)] = "abc"; // 1

   w[Point(buffer,0)] = ? // 2

I believe that in line 2, result should always be "abc" (since
Point(buffer, 0) === Point(buffer, 0)).
This is something we can spec, but it is probably not behavior we want.

Dmitry
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