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Appending anonymous function pointer to slice overwrites previous pointers #43565

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soypat opened this issue Jan 7, 2021 · 1 comment
Closed

Appending anonymous function pointer to slice overwrites previous pointers #43565

soypat opened this issue Jan 7, 2021 · 1 comment
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@soypat
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soypat commented Jan 7, 2021

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

$ go version
go version go1.15.6 windows/amd64

Does this issue reproduce with the latest release?

15.6 is latest release I believe.

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

go env Output
$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\grade\AppData\Local\go-build
set GOENV=C:\Users\grade\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\grade\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\grade\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=0
set GOMOD=C:\Users\grade\Documents\src\godesim\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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\grade\AppData\Local\Temp\go-build485996670=/tmp/go-build -gno-record-gcc-switches

What did you do?

MWE: https://play.golang.org/p/aV6OpQwtc4K

package main

import (
	"fmt"
)

func main() {
	var x  = []func(){
		func() { fmt.Println("First printer") },
		func() { fmt.Println("Second printer") },
		func() { fmt.Println("Third printer") },
	}
	
	var y = make([]*func(),0)
	for _, v := range x {
		y = append(y, &v) // append pointers to slice
	}
	for _, v := range y {
		(*v)()
	}
}

Full example with comments on why this is counterintuitive:
https://play.golang.org/p/aFDUcEGu2zV

What did you expect to see?

First Printer
Second Printer
Third Printer

What did you see instead?

Third printer
Third printer
Third printer
@soypat soypat closed this as completed Jan 7, 2021
@soypat
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soypat commented Jan 7, 2021

v's value is changed on every iteration and since I'm passing a pointer, so are they

@soypat soypat mentioned this issue Jan 8, 2021
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@golang golang locked and limited conversation to collaborators Jan 7, 2022
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