The language specification https://go.dev/ref/spec#Method_sets states that
The method set of an interface type is the intersection of the method sets of each type in the interface's type set
but the following program shows something different:
package main
type A int
func (A) A()
type I interface {
A
}
func F[T I](a T) {
a.A() // Can't compile
}
The type set of I consist type A only, so the method set of I should be the method set of A .
It should compile.
go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\user\AppData\Local\go-build
set GOENV=C:\Users\user\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\user\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\user\go
set GOPRIVATE=
set GOPROXY=https://goproxy.cn,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.23.1
set GODEBUG=
set GOTELEMETRY=local
set GOTELEMETRYDIR=C:\Users\user\AppData\Roaming\go\telemetry
set GCCGO=gccgo
set GOAMD64=v1
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=NUL
set GOWORK=
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=C:\Users\user\AppData\Local\Temp\go-build3096620470=/tmp/go-build -gno-record-gcc-switches
Comment From: gabyhelp
Related Issues and Documentation
- spec: method set of an interface type #52321 (closed)
- spec: Method sets section doesn't seem quite right for interfaces with type lists #51183
- cmd/compile: suggest clearer error regarding when a non-pointer type cannot be used as type parameter #51515
- Confirm the visibility of Method Sets #16421 (closed)
- spec: interfaces that have different-size method sets never unify (but they possibly could) #57192 (closed)
- The Go Programming Language Specification > Types > Method sets
- Cascading `interface` definitions — interfaces containing methods using other interfaces — seem to break. #66767 (closed)
- spec: Interface method specifiers #10291 (closed)
- generics: method-on-generic-type shadowing an existing type can lead to surprising method sets #58100 (closed)
- Table of Contents > The Spec
(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)
Comment From: zigo101
It is the temporarily status quo of Go custom generics: https://go101.org/generics/888-the-status-quo-of-go-custom-generics.html