Sorry to drag on about array holes, but: Should holes in spread elements (e.g. [...holeyArray]) and arguments (e.g. f(...holeyArray)) reflect as holes in the array they are spliced into to avoid information loss ? The current proposal [1] reflects them as `undefined` values.
Spread arguments will reflect in both the `arguments` array and the rest parameter binding if there is one, so this would allow them to have holes. The only issue I see is that Function.prototype.apply reflects holes as `undefined` values in the `arguments` array, so if `f` is a function whose code loops over `arguments` skipping holes (most likely via ES5 Array extras), then the following migration could cause holes to be skipped which were previously not: f.apply(holeyArray) -> f(...holeyArray) This should be rare, since for one thing holey arrays are rare, and it's unlikely anything important was being done with the `undefined` values which are now being skipped. If this is an issue, the holes could only be reflected in rest parameter bindings since they are meant to replace `arguments` in the long run anyways. On a separate note, I'm not sure if argument lists should be made symmetric to array element lists, by allowing them to have holes (e.g. f(1, , 3)), but it would essentially allow `undefined` arguments to be ommitted, if that would be considered useful. [1] http://wiki.ecmascript.org/doku.php?id=harmony:spread Thanks, Sean Eagan _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
