On Mon, Jan 28, 2013 at 3:59 PM, Mark Miller <erig...@gmail.com> wrote:
> Tor this[symbol] = value or equivalent on one side of a membrane, followed > by this[symbol] or equivalent on the other side of the membrane, we have > the following eight cases. > That should be "For thing[symbol] = value or equivalent...by thing[symbol] or equivalent..." > > For all of these, o1 is the original non-proxy thing associated with the > private properties. > p1 is the proxy result of passing o1 through a membrane > o2 is a PrivateSymbol or WeakMap > p2 is the result of passing o2 through a membrane. > When o2 is a WeakMap, p2 is a proxy for the WeakMap. > When o2 is a PrivateSymbol, p2 is a PrivateSymbol that the membrane > considers to correspond to o2 > o3 is the original non-proxy value to be stored in this private property. > p3 is the proxy result of passing o3 through the membrane. > > o1[o2] = o3; p1[p2] // undefined !== p3 > o2.set(o1, o3); p2.get(p1) // p3 > > o1[o2] = p3; p1[p2] // undefined !== o3 > o2.set(o1, p3); p2.get(p1) // o3 > > o1[p2] = o3; p1[o2] // undefined !== p3 > p2.set(o1, o3); o2.get(p1) // p3 > > The remaining 5 cases are left as an exercise for the reader ;). > > The reason they all work for WeakMaps is that the WeakMap itself is on one > side of the membrane and both gets and sets go there. The weakmap only sees > the thing and value on its side of the membrane. The requestor only sees > the thing and value on their side of the membrane. > > The reason none of these work under proposal #2 is that the > thing[privateSymbol] operations on one side of the membrane don't make it > to the other side. > > The reason none of these work under proposal #1 is that the > thing[privateSymbol] operations don't trap, and so the membrane doesn't get > to wrap or unwrap the stored value. > > > > On Mon, Jan 28, 2013 at 1:21 PM, Mark S. Miller <erig...@google.com>wrote: > >> On Mon, Jan 28, 2013 at 11:52 AM, Andreas Rossberg >> <rossb...@google.com>wrote: >> >>> On 28 January 2013 19:45, Tom Van Cutsem <tomvc...@gmail.com> wrote: >>> > I just wrote up a strawman on the wiki to summarize the recent debates >>> about >>> > the interaction between proxies and private symbols: >>> > >>> > http://wiki.ecmascript.org/doku.php?id=strawman:proxy_symbol_decoupled >>> > >>> > The page actually lists two proposals, out of which I prefer the >>> second one. >>> > >>> > If I forgot some benefits/drawbacks of either approach, please speak >>> up. >>> >>> Under the second approach, how can you transparently proxy an object >>> with private properties _at all_? It seems like you can't, even when >>> you have access to its private names. In other words, what do you mean >>> by "inherit the private state of the target", when the target is still >>> aliased and accessed? >>> >> >> >> There is an interesting difference between weakmaps and Tom's second >> proposal. >> >> >> ----------------------------------------------------- >> Consider, in proposal #2: >> >> // All on the wet side of the membrane. No interesting difference yet >> >> var wetRecord = { >> symbol: PrivateSymbol(), >> thing: whatever() >> }; >> var wetValue = whatever() >> wetRecord.thing[wetRecord.symbol] = wetValue; >> >> // transition to dry side >> >> var { wrapper: dryRecord, gate } = makeMembrane(wetRecord); >> >> var dryValue = dryRecord.thing[dryRecord.symbol]; >> >> // Under proposal #2, dryValue is undefined >> ----------------------------------------------------- >> >> >> >> >> ----------------------------------------------------- >> Now let's do the "same" thing with WeakMaps: >> >> // All on the wet side of the membrane. No interesting difference yet >> >> var wetRecord = { >> symbol: WeakMap(), >> thing: whatever() >> }; >> var wetValue = whatever() >> wetRecord.symbol.set(wetRecord.thing, wetValue); >> >> // transition to dry side >> >> var { wrapper: dryRecord, gate } = makeMembrane(wetRecord); >> >> var dryValue = dryRecord.symbol.get(dryRecord.thing); >> >> // dryValue is a proxy for wetValue >> ----------------------------------------------------- >> >> >> >> Conclusion: Although both WeakMaps and Private Symbols have "issues" when >> virtualized through membranes, WeakMaps virtualize usefully under more >> scenarios than do Private Symbols under proposal #2. >> >> >> -- >> Cheers, >> --MarkM >> >> _______________________________________________ >> es-discuss mailing list >> es-discuss@mozilla.org >> https://mail.mozilla.org/listinfo/es-discuss >> >> > > > -- > Text by me above is hereby placed in the public domain > > Cheers, > --MarkM > -- Cheers, --MarkM
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