sorry, that last sentence of the second paragraph should be "The structural comparison says they *are* identical".
On Fri, May 8, 2020 at 6:19 PM Axel Wagner <axel.wagner...@googlemail.com> wrote: > Correct. I don't understand why you are saying that, though. > The argument I'm making is that x and y's *types* (not underlying) types > are identical (actually, the argument I *was* making was different, but > still had little to do with underlying types). > > The spec <https://golang.org/ref/spec#Type_identity> says > > A defined type is always different from any other type. Otherwise, two > types are identical if their underlying type literals are structurally > equivalent; that is, they have the same literal structure and corresponding > components have identical types. In detail: > Now, as neither x's nor y's types are defined, the first sentence doesn't > apply. So we have to compare the structure of their underlying types. The > relevant part of that list is > > Two channel types are identical if they have identical element types and > the same direction. > So we have to check whether `error` and `interface{ Error() string }` are > identical. And that's where the question of whether error is a defined type > comes in (as I said, I'd argue that with the spec as-is it *probably* > isn't. It's at least not clearly stated). > If `error` is defined, then the two types are different; a defined type is > different from any other type. > If `error` is *not* defined, then we fall back to comparing the structure > of their underlying types. The structural comparison says they *are* > different. > > So, really, using channels was maybe a bit of a red-herring. As I said, > the argument I was making still applies. But the argument that `error` and > `interface{ Error() string }` *should* be identical if error is not defined > is easier to make. > > On Fri, May 8, 2020 at 6:08 PM Jan Mercl <0xj...@gmail.com> wrote: > >> On Fri, May 8, 2020 at 5:57 PM Axel Wagner >> <axel.wagner...@googlemail.com> wrote: >> > >> > I'm happy to report, that I *think* I found an inconsistency with error >> not being a defined type: >> > https://play.golang.org/p/gpy6S17wzIM >> >> I don't follow. Type of x is not a defined type and neither is type of >> y. The underlying type of x is not the same as the underlying type of >> y. >> > -- 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/CAEkBMfFnpYBH%3Dj821MQpNmBEU3dbz4_dJYf%2B3hBi0B5j5XH4Lw%40mail.gmail.com.
