To answer the subject line question: No, short variable declarations are not technically necessary. We could have chosen not to have them. But there are good reasons for them. It was a deliberate design decision.
Let me throw in a bit of historical perspective: Rob's invention of ":=" in one of his prior languages, and later, our shared experience with ":=" in Sawzall ( https://en.wikipedia.org/wiki/Sawzall_(programming_language)) led to the desire of wanting ":=" in Go. Variable declaration and initialization is among the most common statements written in an imperative programming language (next to simple assignment), and ":=" worked beautifully and succinctly for this purpose in the past, and it fit well into the overall design of Go. The key here is that providing an initialization expression is mandatory with ":=" (in contrast to "just" a variable declaration), and because it's mandatory, we can omit the type of the variable (assuming we're ok with the type of the initialization expression). At the same time we wouldn't simple give up ordinary variable declarations, using the "var" keyword. For one, at the package level, a free-standing (i.e., w/o introductory keyword) "v := x" would cause parsing difficulties and be somewhat irregular compared to all other declarations. Thus, originally, "x := y" was simply very convenient syntactic sugar for "var x = y" and both could be used interchangeably, in most places. Go has little syntactic sugar, and where it has, it's because there's a lot of "bang for the buck" - and that's certainly the case for ":=". The fact that "var x = y" is not permitted as a "for" loop initialization statement was simply a design decision. Ian Taylor suggested that it's "ugly". Aesthetics plaid a role here; and different people find different things attractive. There's no hard technical reason why it couldn't be permitted, it just isn't. Finally, the special rule permitting "redeclarations" with ":=" only came in later. It gave short variable declarations different powers over regular keyword-based variable declarations. While it was considered a very useful new rule, it definitively distracted from the simple syntactic sugar regularity. It is no secret that many people (including us) think that there may be too many different yet similar ways of declaring and initializing variables in Go; and it would be nice if a future Go could streamline and simplify this. But we should also keep in mind that variable declaration and initialization, next to simple assignment, are the most common statements in program (it's one of the few things hardware can actually do directly, which is moving data from a to b), so it does not seem unreasonable to have various ways to express that, fine-tuned for each (relatively common) use case. - gri On Thu, Oct 20, 2016 at 12:19 AM, T L <tapir....@gmail.com> wrote: > > > On Thursday, October 20, 2016 at 3:25:18 AM UTC+8, Ian Lance Taylor wrote: >> >> On Wed, Oct 19, 2016 at 11:38 AM, Michael Jones <michae...@gmail.com> >> wrote: >> > As in a number of previous questions, this one was asked poorly and the >> answers dance all around the intention. I had decided never to enter the >> fray of these oddly-put assertion/half questions, but since this is >> lingering, may I suggest that this is his real question: >> > >> > “can we have var-style declarations in the places where the shorthand >> syntax is allowed?” >> > >> > elaborating… >> > >> > for i := 0; i < 10; i++ {…} >> > >> > might also allow >> > >> > for var i int; i < 10; i++ {…} >> > >> > and likewise in other short-variable-permitting contexts. >> > >> > Personally, it seems that the simplest argument in favor would be >> orthogonality and the best argument in favor would be the natural creation >> of multiple scope local variables. This “best” is not very strong, though, >> since it is unclear to me how you could introduce variables of multiple >> types. >> > >> > Not taking sides here…just feeling that the core issue was not >> addressed. Nor was the much better question that was not asked, “why was >> the decision made in Go not to allow non-short variable declarations in >> these contexts?” >> >> Thanks for trying to clarify. >> >> I'm not sure I buy the orthogonality argument here. I mean, why not >> permit any statement in the first clause of a for statement? Why >> restrict it to just variable declarations? But if we accept that it >> is restricted, I think it seems reasonable to restrict only to short >> variable declarations, since `for var i int` seems to me to be ugly. >> >> You can create multiple local variables in the for scope by writing, for >> example >> for a, b := 0, 10; a < b; a++ { >> (That would work with var, too). >> >> Ian >> > > I think the short form should be used as a supplement for the normal var > form, > Specifically, short form should be used in the situation new variable > identifiers and old variable identifiers are hybrid, > or the situation only new variable identifiers exist. > > But now, the short form in an inner block will shadow variables in outer > block. > If we really want to shadow variables in outer block, then we can just use > the normal var form. > Now the design makes the short form compete with the normal var form. > > > > -- > 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. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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