Hi, I'll note that this has nothing, really, to do with the loop, but with the fact that you are assigning a struct field. For a simpler example, compare this: https://go.dev/play/p/MmR-AhOUQH3 with this: https://go.dev/play/p/Y1uoI8thYuV If you only write to the entire variable, the compiler complains about that variable not being used. But if you set a field, the failure goes away.
This compilation error is based on this sentence from the spec <https://go.dev/ref/spec#Variable_declarations>: > Implementation restriction: A compiler may make it illegal to declare a variable inside a function body <https://go.dev/ref/spec#Function_declarations> if the variable is never used. Note that it says "may" make it illegal. It's also not really defined what it means for a variable to be "never used". TBH I don't really like these implementation-defined compilation failures. But it would be difficult to make them more strict. Perhaps this case could be a vet warning. On Mon, May 6, 2024 at 4:20 PM Tiago de Bem Natel de Moura < t.nateldemo...@gmail.com> wrote: > Hello, > > We had the bug below in production: > https://go.dev/play/p/-jewy7e7UcZ > > Look at the `opt` variable inside `listGithubPullReviews`, it's set > multiple times (inside the loop) but never used... it was supposed to be > passed as the last argument of `ListReviews()`. > > Why Go compiler is not giving an error for this case? AFAICS all of those > `opt.Page = resp.NextPage` inside the loop cannot make any side effects, > then it looks safe to assume the variable is only set and never used? > > So, simplifying the problem, this is the non-failing case: > https://go.dev/play/p/FLAIlVx_sSG > > But if you change from a struct to a plain int, then the compiler gives: > `./prog.go:6:2: > a declared and not used` > > Luckily, we were using a `ctx` with timeout otherwise it would be an > infinite loop. The thing was tested but only for cases where all results > came in a single page, then the loop aborted in the first iteration. I > think this could be detected by the compiler, no? > > -- > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/9a2b5179-f083-4365-b0c6-e876f3fe6950n%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/9a2b5179-f083-4365-b0c6-e876f3fe6950n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAEkBMfECnnFQkdwSn3gqzRxHL7MnkfoUvABFg8xr0B-9jTkSjQ%40mail.gmail.com.
