On Nov 11, 2011, at 3:17 PM, David Herman wrote: > Late to the party, but I've brought more booze. > > On Nov 5, 2011, at 2:41 PM, Brendan Eich wrote: > >> We have: >> >> 1. Should an array pattern always query 'length'? >> >> 2. If the answer to (1) is "no", then should ... in an array pattern query >> 'length'? >> >> On reflection and at this point in the thread, with your reply in mind, my >> prefs in order: [no, yes], [no, no]. In no case do I favor [yes]. I'm >> refutably matching [no, _] :-P. > > I feel strongly that the appropriate semantics is [no, yes].
Pretty much the conclusion I also came to: On Nov 7, 2011, at 8:53 AM, Allen Wirfs-Brock wrote: > Yes, as I mentioned in another reply array [ ] access doesn't check length. > But "slicing" operations including Array.prototype.slice and > Function.prototype.apply (slices from 0 to length) all do use length. > > That is way [no, yes] may actually be the most consistent approach. > ... > > A pattern of the form > > [a0, a1, 〰〰, ak, ...r] > > desugars to > > a0 = %v[0]; > a1 = %v[1]; > 〰〰 > ak = %v[k]; > let %length = %v.length; do we sample the length here or at the very beginning? It presumably only matter if a %v[n] is an accessor with side-effects that modify %v. Generally, the array functions sample length at the beginning before processing any elements. > r = [ %v[i] for i of [k+1, 〰〰, %length - 1] if (i in %v) ]; > > This can be generalized further to allow a fixed number of patterns *after* > the ellipsis as well: > > A pattern of the form > > [a0, a1, 〰〰, ak, ...r, bn, bn-1, 〰〰, b0] We currently haven't specified this syntactic form. I'm not sure if it adds enough value to justify the added conceptual complexity. Allen _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
