On Friday, October 14, 2016 at 12:49:43 AM UTC+8, Ian Lance Taylor wrote: > > On Thu, Oct 13, 2016 at 9:40 AM, <di...@veryhaha.com <javascript:>> > wrote: > > > > On Friday, October 14, 2016 at 12:14:34 AM UTC+8, Ian Lance Taylor > wrote: > >> > >> On Thu, Oct 13, 2016 at 8:36 AM, <di...@veryhaha.com> wrote: > >> > > >> > On Thursday, October 13, 2016 at 11:24:50 PM UTC+8, Jesper Louis > >> > Andersen > >> > wrote: > >> >> > >> >> The rule is that a short variable declaration requires that at least > >> >> one > >> >> non-blank variable is new (the specification even says so) Consider > >> >> > >> >> _, y := 4,5 > >> >> > >> >> where one variable, y, is new. In > >> >> > >> >> _ := 6 > >> >> > >> >> or > >> >> > >> >> _, _ := 5, 7 > >> >> > >> >> this rule is violated, since there are no non-blank variables (and > thus > >> >> vacuously nothing new). > >> >> > >> >> I think the reason this is a rule is because it may detect some > >> >> spurious > >> >> errors by forcing the programmer to write code in a certain style, > but > >> >> I may > >> >> be wrong. > >> > > >> > > >> > > >> > What spurious errors? > >> > >> The error of thinking that because you are using := you are getting a > >> new variable. > >> > >> The handling of := is a bit tricky, perhaps too tricky. It used to > >> always declare new variables, and give an error if there was already a > >> variable of the same name in the same scope. But that was too painful > >> to use with the err variable, because of the common use of > >> n, err := F() > >> So := was changed to permit reusing a variable if it already existed > >> in the same scope with the same name and (inferred) type. > > > > > > But the long variable declaration form only allows all variables are new > > ones generally, except for the blank _ identifier. > > Why not also make an exception for the blank _ identifier in the short > form? > > Every language change has a cost and a benefit. The cost of this > change is that right now we have a simple rule: a := statement must > define at least one new variable. You are suggesting that we replace > that with a more complicated rule: a := statement must define at least > one new variable, except in the case where all the variables are the > blank identifier, in which case it is OK. Also, the language is > stable, so any change at all carries a cost. The benefit of this > particular change seems to me to be very very small: when you have an > existing `a, _ := b, c` statement, you can change it to `_, _ := b, c` > instead of changing it to `_, _ = b, c`. I don't see why the very > small benefit outweighs the cost. > > I'm just speaking for myself, of course. If this is important to you, > you could write this up as a language change proposal, describing the > change and presenting an argument for why the benefit outweighs the > cost. See https://github.com/golang/proposal . But I suspect that > such a proposal would be rejected unless the argument in favor was > quite convincing. > > Ian >
yes, I have filed one: https://github.com/golang/go/issues/17429 and yes, it was rejected. I admit this is really not a big problem. -- 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.
