On Fri, Jul 1, 2016 at 2:42 AM, Martin Geisler <mar...@geisler.net> wrote: > > On Mon, Jun 27, 2016 at 8:18 PM, Ian Lance Taylor <i...@golang.org> wrote: >> On Sun, Jun 26, 2016 at 10:55 PM, Dan Kortschak >> <dan.kortsc...@adelaide.edu.au> wrote: >>> On Mon, 2016-06-27 at 07:49 +0200, Martin Geisler wrote: >>>> BTW, I was about to say that you could simplify the line one step >>>> further with >>>> >>>> b := append(a[::len(a)], 3, 4) >>>> >>>> but that gives a compilation error: >>>> >>>> prog.go:11: middle index required in 3-index slice >>>> >>>> I wonder what the rationale is for this? It seems inconsistent to me >>>> since the second (middle) index has a useful default (len(a)) that is >>>> used when there are only two indexes used. >>> >>> As I remember it, during the design discussions the possibility of using >>> the shortened syntax you show above was considered, but rejected as an >>> opening to bug entry (too much semantic weight on a single repeated >>> character). >> >> Yes. And, also, the default for the middle index is not wholly >> obvious. Should it be len(a) or (new) cap(a)? In your example those >> happen to have the same value, but of course in general they do not. > > Hmm, that's a good point that I hadn't considered :-) I figured it > would be len(a) so that > > a[x::z] = a[x:len(a):z] > > That keeps the defaults intact from normal 2-index slicing. > > For the indices to be in range, you must have z >= y where y = len(a). > So maybe one could argue that the middle index y could be clamped at > z, that is, the middle index y could be set to min(z, len(a)). That > way you can have a slice with length 10 and still write > > a[2::4] = a[2:min(4, 10):4] = a[2:4:4] > > where there indices are all in range. > > I see how this becomes more complicated than I initially thought... is > that the kind of mess you were thinking of? :-)
Yes, that is an example. If there is a default, it should be obvious in all cases what the default should be. If it's not obvious, there shouldn't be a default. Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
