Just to clarify: This is not directly related to generics. It is related to interfaces (and the type constraints feature) which are incidental to generics and provides extra power to developers. In this particular use case, it provides a useful compile-time check for an argument that is intended to be a generic struct.
On Thursday, June 25, 2020 at 9:34:35 AM UTC+10, Pee Jai wrote: > > I disagree. A type constraint for a struct would definitely provide > compile-time guarantee that only a struct can be used. > > On Thursday, June 25, 2020 at 8:18:13 AM UTC+10, Ian Lance Taylor wrote: >> >> On Wed, Jun 24, 2020 at 12:22 PM David Finkel <david...@gmail.com> >> wrote: >> > >> > On Wed, Jun 24, 2020 at 9:34 AM Robert Engels <ren...@ix.netcom.com> >> wrote: >> >> >> >> Generics will not solve this fully anyway - you’ll still need >> reflection. Why not just return empty if the user doesn’t pass a struct? >> >> >> > That sounds like a bug waiting to happen. >> > >> > I have a library with a similar reflection-related use-case involving >> reflection, which currently panics when it gets a non-struct-type. It would >> be nice to have compile-time type-checking, if possible. >> >> >> Generics don't solve all problems. I'm inclined to say that this is a >> problem that they don't solve. Sorry. >> >> Ian >> >> >> >> >> >> On Jun 24, 2020, at 8:29 AM, Pee Jai <p...@pjebs.com.au> wrote: >> >> >> >> >> >> Here is my use case: >> https://godoc.org/github.com/rocketlaunchr/react#UnmarshalState >> >> >> >> That function has an argument that accepts only a struct. I use the >> reflect package to iterate over the structs fields (and also to check if it >> actually is a struct). The function has notapplicability for non-structs. >> >> >> >> Currently I have to notify the user via documentation that only a >> struct is allowed since the type is officially an `interface{}`. This is >> very crude. >> >> >> >> If there was a way to add a type constraint for only structs, then I >> don't need to use documentation, notwithstanding the use of reflect package >> to iterate over the struct fields. >> >> >> >> On Wednesday, June 24, 2020 at 10:34:40 AM UTC+10, Ian Lance Taylor >> wrote: >> >>> >> >>> On Mon, Jun 22, 2020 at 7:08 PM Pee Jai <p...@pjebs.com.au> wrote: >> >>> > >> >>> > I can't find a way to constrain for just structs. I don't want >> primitives. >> >>> >> >>> The design draft doesn't provide any mechanism for a type constraint >> >>> to match any arbitrary struct type, and not any other kind of type. >> >>> >> >>> But it's not clear why that would be useful. The only things you can >> >>> do with a value of an arbitrary struct type are things that you can >> do >> >>> with a value of any arbitrary type. >> >>> >> >>> 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 golan...@googlegroups.com. >> >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/e86e677b-784d-47c5-b8b9-aedc37977ba5o%40googlegroups.com. >> >> >> >> >> >> -- >> >> 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 golan...@googlegroups.com. >> >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/8013EEB8-78E6-455D-B846-8A826682B879%40ix.netcom.com. >> >> >> > >> > -- >> > 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 golan...@googlegroups.com. >> > To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/CANrC0BgyoPvEWJEOOrJwt-3qfLvSxc6CX9yLoYBPxYZV8GBZLg%40mail.gmail.com. >> >> >> > -- 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/2f8db812-077d-4955-a2ec-78657af1ec45o%40googlegroups.com.
