Would it suffice to allow cross-frame sharing of symbols via postMessage and its structured clone algorithm? They're immutable, right?
On Oct 3, 2012, at 15:01, "Brendan Eich" <[email protected]> wrote: > Thanks for pointing this out. Python's dunder-prefixing or anything like it > in JS has that advantage: you can spell the magic property name with a string > that works in any frame or global object. Of course strings can collide. > > Symbols are useful in spite of this, but it is telling that we want @iterator > to be a singleton across all potentially connected frames. > > So should there be a way in the language to create singleton symbols? If so, > how? > > /be > > Kevin Smith wrote: >> One of the main use cases for symbols is for defining object "protocols" >> that don't suffer from property name conflicts. The recently discussed >> `iterator` and `toStringTag` method names fall into this category. The idea >> is that we can implement the protocol by defining methods using symbols, and >> thus avoid namespacing considerations. >> >> Designing and maintaining a global namespace is, well, no fun. >> >> But consider the multiple-global case in which we have scripts running in >> more than one frame. It seems like protocols should be transferrable across >> frames. For built-in protocols like `iterator`, this has to work: >> >> function f(iterable) { >> for (x of iterable) { >> // This must work regardless of which frame `iterable` comes from >> } >> } >> >> But what about user-defined protocols? Let's say we have a "Persistable" >> protocol: >> >> export var persistName = new Symbol; // unique, not "private" >> >> And a function which makes use of this protocol: >> >> import persistName from "Persistable.js"; >> >> function usePersistable(obj) { >> >> if (obj[persistName]) >> obj[persistName](); >> } >> >> It seems like `usePersistable` should be able to work as expected even if >> `obj` comes from a different frame (in which "Persistable.js" was separately >> loaded). >> >> Another expression of the same problem occurs with versioning. >> >> Suppose that in a fairly complex module dependency graph, >> "Persistable-0.1.js" and "Persistable-0.2.js" are simultaneously loaded. >> ("Persistable" is on github and therefore in perpetual version-zero >> purgatory.) It seems reasonable to expect that objects implementing the >> protocol defined by "Persistable-0.2.js" should be able to work with >> functions consuming the "Persistable-0.1.js" protocol. But that is not >> possible with unique symbols. >> >> In summary, I don't think that we can really avoid global namespacing issues >> using system-generated unique symbols as we currently conceive of them. >> Built-in protocols like `iterator` are a special "cheating" case, but we >> need to have an equally consistent story for user-defined protocols. >> >> Kevin >> >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
