Brendan Eich wrote: > Nathan Wall wrote: > > In the case of (2), the implementation using a private symbol will fail on > > a call to `setTime` when the object is frozen (I think). > > Nope, we agreed that frozen objects support setting pre-existing (added > before the object was made non-extensible) properties named by private > symbols.
I wasn't aware, but that significantly improves the case for symbols. I'm glad to hear it! However, it also begs the question of why symbols should behave differently from WeakMaps/closures in the presence of Proxies (via unknownPrivateSymbol trap). David Bruant wrote: > > In the case of (1), the implementation using a private symbol will have > > internal accesses to the `timestamp` symbol exposed through the > > unknownPrivateSymbol trap. > The trap does not expose the symbol. That would be a bad leak. > The third "whitelist" argument in the proxy constructor is here to > communicate whether the proxy knows the privatesymbol or not. > When [[Get]] or [[Set]] (or other property operations) happens with a > whitelisted private symbol, the get or set (or other) trap is called > with the symbol itself (since it's known). If the name isn't in the > whitelist, the unknownPrivateSymbol trap is called with target as the > *only* trap argument (the private name is not exposed and that's on > purpose!) I'm sorry, I was unclear. I understand that the symbol itself is not exposed, but the fact that some symbol was accessed is. It wold allow a proxy to throw to prevent access to internal state (right?). This is different from what would occur in the WeakMap implementation, and if I'm trying to hide internal state, then I don't want proxies to be able to mess with attempts to access it, so I'll choose to use WeakMaps anytime I want to write defensive code. Of course, if I'm just writing something quick and dirty, I'll use Symbols because I would much prefer to use the simpler syntax Symbols provide. But again, as a library author, allowing Proxies to interfere here seems like a weaker position for a generic object than using a WeakMap to hide this. Nathan _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
