variables modified by later parameters are unreliably updated

[urandom2]

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

$ go version
go version go1.12 linux/amd64

Does this issue reproduce with the latest release?

yes

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

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/user/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/user/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build021705053=/tmp/go-build -gno-record-gcc-switches"

What did you do?

var a []int
var b bool
var c complex64
var f float32
var i int
var m map[int]int
var r rune
var s string
var t struct{ i int }
var u uint

fmt.Println(a, b, c, f, i, m, r, s, t, u, func() string {
	fmt.Println(a, b, c, f, i, m, r, s, t, u, "first")
	a = []int{1}
	b = true
	c = complex(1, 1)
	f = 1
	i = 1
	m = map[int]int{1: 1}
	r = '1'
	s = "1"
	t = struct{ i int }{1}
	u = 1
	fmt.Println(a, b, c, f, i, m, r, s, t, u, "second")
	return "third"
}())

play

What did you expect to see?

either:

[] false (0+0i) 0 0 map[] 0  {0} 0 first
[1] true (1+1i) 1 1 map[1:1] 49 1 {1} 1 second
[] false (0+0i) 0 0 map[] 0  {0} 0 third

or

[] false (0+0i) 0 0 map[] 0  {0} 0 first
[1] true (1+1i) 1 1 map[1:1] 49 1 {1} 1 second
[1] true (1+1i) 1 1 map[1:1] 49 1 {1} 1 third

What did you see instead?

[] false (0+0i) 0 0 map[] 0  {0} 0 first
[1] true (1+1i) 1 1 map[1:1] 49 1 {1} 1 second
[1] false (0+0i) 1 1 map[] 49 1 {1} 1 third

[winjeg]

The result for me on go 1.11.5 ran on my PC is as follows

[] false (0+0i) 0 0 map[] 0  {0} 0 first
[1] true (1+1i) 1 1 map[1:1] 49 1 {1} 1 second
[] false (0+0i) 0 0 map[] 0  {0} 0 third

It seems like a bug on go playground.

GO ENV

set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\wenwen\AppData\Local\go-build
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\wenwen\go
set GOPROXY=
set GORACE=
set GOROOT=D:\apps\goinst
set GOTMPDIR=
set GOTOOLDIR=D:\apps\goinst\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=D:\projects\go\github.com\winjeg\demo\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\wenwen\AppData\Local\Temp\go-build471180878=/tmp/go-build -gno-record-gcc-switches

[urandom2]

I can reproduce this on my local system too, the play link is for ease of access.

[zigo101]

The evaluation order of non-function expressions and function expressions is not specified in a statement. See

• proposal: spec: reduce unspecified behaviors of expression evaluation orders in assignment statements #27804
• https://github.com/go101/go101/wiki/Some-evaluation-orders-in-multi-value-assignments-are-unspecified
• https://go101.org/article/evaluation-orders.html

[urandom2]

unfortunate that behaviour changed between releases, but this seems like a pretty clear cut duplicate, thanks @go101