Damn, forgot the reply-all button the first time. Including the original and reply here, plus my reply inline:
On Tue, 6 Oct 2015 at 19:05 Tab Atkins Jr. <[email protected]> wrote: > On Mon, Oct 5, 2015 at 6:33 AM, Andy Earnshaw <[email protected]> > wrote: > > On Sat, 3 Oct 2015 at 00:27 Tab Atkins Jr. <[email protected]> wrote: > >> A few examples of the ambiguity: > >> > >> function f1(...a, b, c) {print arguments} > >> f1(1) // ([], 1, undefined) or ([], undefined, 1) ? > >> > >> function f2(...a, b="default") {print arguments} > >> f2(1) // ([], 1) or ([1], "default") ? > >> > >> function f3(a, b, ...c, d, e) {print arguments) > >> f3(1,2,3) // (1, 2, [], 3, undefined) or (1, 2, [], undefined, 3) or > >> (1, undefined, [], 2, 3) or something else? > > > > > > I don't think these are as ambiguous as you say. For the first and third > > case, the first possible result you mention in both cases seems pretty > > natural. I don't think you could make an argument for the other cases, > they > > don't really make any sense. > > Let me rename the arguments, then, to make it more obvious: > > function f1(...frontOfList, secondToLast, last) {print arguments;} > f1(1) > // (frontOfList=[], secondToLast=1, last=undefined) > // or (frontOfList=[], secondToLast=undefined, last=1)? > > It would be difficult to argue, given these argument names, that the > author intended the first result. They clearly intended the second > result. > Function arguments are always filled in from left to right, with the proposed exception in this case being that rest params don't swallow passed in arguments when arguments.length <= fn.length. I don't think anyone coming from a background in writing code would expect the second result, any more than they would expect: function f1 (first, last) { print arguments; } f1(1); // (first=undefined, last=1) Unless there's a precedent for this behaviour in a language I'm unaware of. > This is what I mean by: > > > You can come up with answers to these questions. What you can't do is > come up with answers that are *obviously correct*. > ~TJ > > I don't know... the first result was "obviously correct" to me ;-). Admittedly, "obviously correct" can be subjective when defining language behaviour.
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