No, it's not possible. Oddly enough, when this functionality was first prototyped in SpiderMonkey many years ago, the iterator protocol *did* pass a boolean to the __iterator__ method (this was before symbols) based on the syntax you were using to unpack the results. This feature was not super useful in practice, and I always thought it was too subtle -- the difference in syntax was really not explicit enough to make it clear to the programmer what was going on. I'm glad it wasn't standardized.
-j On Sun, May 22, 2016 at 12:55 PM, Šime Vidas <[email protected]> wrote: > Say I have an array over which I need to iterate multiple times, but I need > the index value only some of the time. Is it possible to create a custom > iterator which auto-detects when I need the index and feeds me entries() > instead of values() in those cases? For example: > > array[Symbol.iterator] = /* some magic here */ > > for (let elem of array) { /* values() iterator is used automatically */ } > for (let [i, elem] of array) { /* entries() iterator is used automatically > */ } > > > _______________________________________________ > 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
