—Claude
Le 14 janv. 2013 à 20:46, Claude Pache <[email protected]> a écrit : > > Le 14 janv. 2013 à 19:29, Kevin Smith <[email protected]> a écrit : > >> >>> >>> The concept of freezing the "whole object" is the problem. If you >>> call `freeze` on a DOM object, does the page stop changing? Of course >>> not -- objects can have hidden state that you, the client of that >>> object, have no access to and thus no way to freeze. This isn't >>> something new being added here. >> >> Slots whose existence is guaranteed to be completely hidden from all code >> that does not possess a "magic key" looks new to me. >> >> You can argue that the change is justified (that's the kind of argument I'd >> like to see in fact), but arguing that it "isn't something new" isn't >> working for me. >> >> { Kevin } >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss > > Really, there is nothing new. In fact, I meant: this sort of behaviour is already implemented in predefined objects, and symbols provide a way to implement it *naturally* in user-defined objects (see below). So there is hopefully something new. > Try this in your favorite ES5-compliant browser: > > d = new Date(2000, 0, 1) > Object.freeze(d) > d // output: Sat Jan 1 2000 ... > d.setFullYear(2001) > d // output: Mon Jan 1 2001 ... Uh? the date was not frozen! > > The value of the Date object is stored in some internal "slot", which is not > enumerable with Object.getOwnPropertyName or configurable with > Object.defineProperty, but only accessed by some ad-hoc API. > > Symbols allow you to store protected properties (just like the date of a Date > object) in a natural manner, without resorting to some clever hack. And the > very definition of "protected" means that you can't access if you haven't the > key. It is really the raison d'être of symbols. > > —Claude
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