affected/package: compiler

[xiazemin]

What version of Go are you using (go version)?

$ go version
go version go1.18beta2 darwin/arm64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE="on"
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/xiazemin/Library/Caches/go-build"
GOENV="/Users/xiazemin/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/xiazemin/.gvm/pkgsets/go1.18beta2/global/pkg/mod"
GONOPROXY="git.shimo.im"
GONOSUMDB="git.shimo.im"
GOOS="darwin"
GOPATH="/Users/xiazemin/.gvm/pkgsets/go1.18beta2/global"
GOPRIVATE="git.shimo.im"
GOPROXY="https://goproxy.cn"
GOROOT="/Users/xiazemin/.gvm/gos/go1.18beta2"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/xiazemin/.gvm/gos/go1.18beta2/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.18beta2"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/xiazemin/source/template_learn/generic/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/hb/1q06vpss7_d1fw3ymxb1ztbr0000gn/T/go-build1495064095=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

type Student struct {
	Name string
}
type Teacher struct {
	Name string
}

func ShowStudent[T Student](s T) {
	fmt.Println(s.Name)
}

func Show[T Student | Teacher](s T) {
	fmt.Println(s.Name)
}

var st Student
st.Name = "hhh"
Show[Student](st)  //this can work

// ShowStudent[Student](st)
//./gen.go:132:14: Student does not implement Student (Student is not an interface)

What did you expect to see?

the two functions can work as the same

What did you see instead?

Show[Student](st) works fine
but ShowStudent[Student](st) not work
./gen.go:132:14: Student does not implement Student (Student is not an interface)

[ianlancetaylor]

I can't recreate the problem on tip. Perhaps it has been fixed, or perhaps I don't understand your description.

Please show a complete failing example on the Go playground at https://go.dev/play. Click on "Go release" and change it to "Go dev branch" to get the current sources. Thanks.

[xiazemin]

the version of Go dev branch is. devel go1.19-5a040c5a36 Thu Mar 10 09:12:04 2022 +0000
my test version is go1.18beta2 darwin/arm64
so I have this problem

in go 1.18

type Student struct {
	Name string
}
func ShowStudent[T Student](s T) {
	fmt.Println(s.Name)
}

works fine.

but in go1.19
there is a compile error
./prog.go:18:16: s.Name undefined (type T has no field or method Name)

my example is

// You can edit this code!
// Click here and start typing.
package main

import (
	"fmt"
	"runtime"
)

type Student struct {
	Name string
}
type Teacher struct {
	Name string
}

func ShowStudent[T Student](s T) {
	fmt.Println(s.Name)
}

func Show[T Student | Teacher](s T) {
	fmt.Println(s.Name)
}

func main() {
	fmt.Println(runtime.Version())
	var st Student
	st.Name = "hhh"
	Show[Student](st) //this can work

	ShowStudent[Student](st)
}

[ianlancetaylor]

./prog.go:18:16: s.Name undefined (type T has no field or method Name)

This was a late change we made to the language spec and compiler for 1.18. See #51576. s.Name is no longer permitted even if all types in the type set have a Name field. Sorry.

[xiazemin]

will you fix the problem in go1.18?

func Show[T Student](s T)
func Show[T Student | Teacher](s T)

when I call it with

Show[Student](st)

only the second function work ,it is confusing

[ianlancetaylor]

I'm sorry, I don't understand exactly what you are saying.

The test case https://go.dev/play/p/Ti1vlIRR8HO?v=gotip, which is based on your test case, works for me using the future Go 1.18.

Do you have a different test case that fails?

[xiazemin]

yes, It works on go1.19-5a040c5a36
but on go1.18beta2 it faild

[davecheney]

@xiazemin you must not post screenshots. Please use links to go.dev, or if that is unavailable to you, text. Thank you in advance for your understanding.

[xiazemin]

https://go.dev/play/p/JutxFuBvujx?v=go1.18beta2

[xiazemin]

it has been fixed in go1.18rc1