On Wed, Apr 2, 2014 at 9:11 PM, Dmitry Lomov <dslo...@chromium.org> wrote:
> > > > On Wed, Apr 2, 2014 at 8:26 PM, Mark S. Miller <erig...@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. > (to put it another way, for "normal" objects/thin pointers, the user cannot construct the new identical thin pointer out of thin air, therefore garbage collection is possible; whereas the typed objects/fat pointers are user-reconstructable at any point of time - so garbage collection is impossible). > > Dmitry >
_______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
