compiler: struct{} pointer comparison

[olegdayo]

Go version

go version go1.24.2 darwin/amd64

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE='on'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN='${HOM}/go/bin'
GOCACHE='/Users/user/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/user/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/5x/nhxw0g1s1yn1zdn2j1rdlh340000gn/T/go-build4058446008=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/user/Desktop/StaticLanguages/high-level/Go/test/go.mod'
GOMODCACHE='/Users/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/user/go'
GOPRIVATE=''
GOPROXY='direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/user/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_amd64'
GOVCS=''
GOVERSION='go1.24.2'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Ran 2 programs:

package main

import "fmt"

type t struct{}

func main() {
	a, b := &t{}, &t{}
	fmt.Println(a == b)
}

package main

import "fmt"

type t struct{}

func main() {
	a, b := &t{}, &t{}
	fmt.Println(a, b)
	fmt.Println(a == b)
}

What did you see happen?

The first output was:

false

The second output was:

&{} &{}
true

And if I use println instead of fmt.Println, both results are false

What did you expect to see?

The same result for both programs

[seankhliao]

https://go.dev/ref/spec#Comparison_operators

Pointer types are comparable. Two pointer values are equal if they point to the same variable or if both have value nil. Pointers to distinct zero-size variables may or may not be equal.

Unlike many projects, the Go project does not use GitHub Issues for general discussion or asking questions. GitHub Issues are used for tracking bugs and proposals only.

For questions please refer to https://github.com/golang/go/wiki/Questions

[gabyhelp]

Related Issues

• fmt.Printf("%p", &a) changes result of pointer of empty struct comparison #68701 (closed)
• runtime: empty struct type pointer comparison varies #73201 (closed)
• Empty struct comparison behavior is inconsistent #43755 (closed)
• cmd/compile: comparison of pointers to zero sized values is inconsistent #52772 (closed)
• fmt: `fmt.Println` change the value of the pointer #51570 (closed)
• new(struct{})==new(struct{}) dissimilarity #36384 (closed)
• gccgo: struct comparison with blank field could be wrong #55142
• go pass by value？ #48788 (closed)
• cmd/compile: empty struct addresses are not equal #23370 (closed)
• gccgo: value comparison with interface is broken #40152 (closed)

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