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Valid syntax that makes absolutely no sense #35603

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essial opened this issue Nov 15, 2019 · 1 comment

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@essial
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@essial essial commented Nov 15, 2019

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

go version go1.13.3 windows/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\lunat\AppData\Local\go-build
set GOENV=C:\Users\lunat\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\lunat\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=1
set GOMOD=
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\lunat\AppData\Local\Temp\go-build376628234=/tmp/go-build -gno-record-gcc-switches

What did you do?

I created a function that (unintentionally) did what the following basic example does:
func DoSomething() (val int) { return val }

What did you expect to see?

A compile error about not returning a value.

What did you see instead?

It compiled and ran fine. Because of variable masking, I was setting a locally scoped variable instead of the return value, which caused it to always return 0.

@ianlancetaylor

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@ianlancetaylor ianlancetaylor commented Nov 15, 2019

That is how the language works. Named result parameters are in scope within the function body. You can assign to them. You can use return with no values to return the values that are currently in the named result parameters (https://golang.org/ref/spec#Return_statements). You can change the values of the result parameters in deferred functions (https://golang.org/ref/spec#Defer_statements).

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