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runtime: Panic, when passing anonymous field, which is a pointer to a named type #20907

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vbauerster opened this issue Jul 5, 2017 · 2 comments
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runtime: Panic, when passing anonymous field, which is a pointer to a named type #20907

vbauerster opened this issue Jul 5, 2017 · 2 comments
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@vbauerster
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Please answer these questions before submitting your issue. Thanks!

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

go version go1.8.3 darwin/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/vbauer/gocode"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.8.3/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.8.3/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/5l/t0s3df6d2w56fq0bhc9tk0k40000gn/T/go-build151792197=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

This code works well, while this one panics. Both compiles without errors.

What did you expect to see?

I expected both code samples to work the same way, because the difference is only the way kPerson structure is declared.

What did you see instead?

Panic when running the second code sample:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0xffffffff addr=0x0 pc=0xc849a]

goroutine 1 [running]:
main.main()
	/tmp/sandbox393635792/main.go:17 +0x1a
@zegl
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zegl commented Jul 5, 2017

When you use var kp kPerson the *Person field is initialised to the default value of a pointer, which is nil.

You need to add kp.Person = &Person{} to get the panicing version to work as you expect it to. Full example.

@vbauerster
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Ok, I see now. Thanks for pointing this out.

@mikioh mikioh changed the title Panic, when passing anonymous field, which is a pointer to a named type runtime: Panic, when passing anonymous field, which is a pointer to a named type Jul 10, 2017
@golang golang locked and limited conversation to collaborators Jul 10, 2018
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@zegl @vbauerster @gopherbot