domenic at domenicdenicola.com (2013-08-25T00:56:56.560Z)
Can somebody (private mail is okay) please clarify this for me? It looks me like there's a proposal to introduce `@@` syntax to support something that's forbidden in most es6 code anyways (`with`)? Or does it have other use cases? Where can I read more about this?
Can somebody (private mail is okay) please clarify this for me? It looks me like there's a proposal to introduce `@@` syntax to support something that's forbidden in most es6 code anyways (`with`)? Or does it have other use cases? Where can I read more about this? Cheers - peter On Wed, Aug 21, 2013 at 1:58 PM, Andreas Rossberg <rossberg at google.com>wrote: > I'm still trying to wrap my head around the idea of introducing an > @@unscopeable property, as discussed at the last meeting. There seem > to be plenty of edge cases: > > * How would it interact with inheritance? > > let p = {a: 1} > let o = {__proto__: p, [@@unscopeable]: ['a']} > let a = 2 > with (o) { > a // 1 or 2? > } > > let p = {[@@unscopeable]: ['a']} > let o = {__proto__: p, a: 1} > let a = 2 > with (o) { > a // 1 or 2? > } > > * How would it affect assignment? > > let o = {[@@unscopeable]: ['a']} > let a = 2 > with (o) { > a = 1 > a // 1 or 2? > o.a // 1 or undefined? > } > a // 1 or 2? > > let p = {a: 1, [@@unscopeable]: ['a']} > let o = {__proto__: p} > let a = 2 > with (o) { > a = 3 > a // 1 or 2 or 3? > o.a // 1 or 3? > } > a // 2 or 3? > > * How would it interact with mutation? > > let o = {a: 1} > let a = 2 > with (o) { > o[@@unscopeable] = ['a'] > a // 1 or 2? > } > > * How would it interact with compound assignment? > > let o = {a: 1} > let a = 2 > with (o) { > a += (o[@@unscopeable] = ['a'], 2) > a // 2 or 3 or 4? > o.a // 1 or 3? > } > a // 2 or 3 or 4? > > * How would it affect the global object? (At least currently, with > scopes and the global scope share the same object environment > mechanism.) > > var a = 1 > this[@@unscopeable] = ['a'] > a // 1 or undefined? > > var a > this[@@unscopeable] = ['a'] > a = 1 > a // 1 or undefined? > > this[@@unscopeable] = ['a'] > </script><script> > var a = 1 > a // 1 or undefined? > > * How would it expose side effects? > > let s = "" > let o = {a: 1} > let u = {get '0'() { s+="0"; return 'a' }, get '1'() { s+="1"; return > 'b' }} > Object.defineProperty(o, @@unscopeable, {get: function() { s += "u"; > return u }}) > > with (o) {} > s // "" or "u" or "u01" or ...? > > with (o) { c; c } > s // "u01" or "u01u01" or ...? > > with (o) { a } > s // "u01" or "u0" or ...? > > with (o) { a+=1 } > s // "u0" or "u00" or "u01" or "u0101" or ...? > > Some of this looks rather whacky, if not unpleasant. > > /Andreas > _______________________________________________ > es-discuss mailing list > es-discuss at mozilla.org > https://mail.mozilla.org/listinfo/es-discuss > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.mozilla.org/pipermail/es-discuss/attachments/20130821/4e894333/attachment.html>