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

$ go version
go version go1.19.2 darwin/arm64

Does this issue reproduce with the latest release?

Yes

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

$ go env 
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="~/Library/Caches/go-build"
GOENV="~/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="~/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="~/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.19.2"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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/sq/szsnndwj6qz7ynp902xhg9rr0000gn/T/go-build4130374379=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I have a base slice with some elements. And I need 2 slices with the same base elements, and some different elements at the end of them, so I used append to add those elements to the base array 2 times, assigning each of them to a new different variable. Something like this:

a := append(base, elem1)
b := append(base, elem2)

The content of a and b after assigning b is the same in both slices. This changes depending on the number .

Here's an example reproducing the error (with a link to the playground with the same code).

package main

import "fmt"

func main() {
	lim := 3
	a := []int{}
	for i := 0; i < lim; i++ {
		a = append(a, i)
	}

	b := append(a, 20)
	fmt.Println(b)
	c := append(a, 30)
	fmt.Println(b)
	fmt.Println(c)
}

https://go.dev/play/p/5IeuvhEOM13

when changing lim value to 2, the behavior is different, a and b have the values I would expect:

What did you expect to see?

the same behavior when assigning the new variables, regardless of the number of elements in the base slice.

with lim:= 2

[0 1 20]
[0 1 20]
[0 1 30]

with lim:=3

[0 1 2 20]
[0 1 2 20]
[0 1 2 30]

What did you see instead?

with lim:= 2

[0 1 20]
[0 1 20]
[0 1 30]

with lim:=3

[0 1 2 20]
[0 1 2 30]
[0 1 2 30]

depending on the number of elements, the first variable I assign takes the value I appended first or second. This is confusing to me. Is this behaviour expected?