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slice expression with low-index out of range and omitted high index doesn't give "slice bounds out of range" error #28731

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dencoded opened this issue Nov 12, 2018 · 2 comments
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slice expression with low-index out of range and omitted high index doesn't give "slice bounds out of range" error #28731

dencoded opened this issue Nov 12, 2018 · 2 comments
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@dencoded
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What version of Go are you using (go version)?

$ go version
go version go1.11.2 darwin/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="/Users/dencoded/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/dencoded/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/9z/xzkhmlmx63nc49srq6glx6cw0000gn/T/go-build613348640=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://play.golang.org/p/GrgeaBAXGkp
This happens only if we specify low-index as len of slice

i.e. this gives proper error:
https://play.golang.org/p/Ax4khdrwotW

What did you expect to see?

panic: runtime error: slice bounds out of range

What did you see instead?

len: 1
cap: 1
[]
@dominikh
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This is working as intended:

For arrays or strings, the indices are in range if 0 <= low <= high <= len(a), otherwise they are out of range. For slices, the upper index bound is the slice capacity cap(a) rather than the length.

@dencoded
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@dominikh well, if it is by design I've learned something new today 👍

@golang golang locked and limited conversation to collaborators Nov 12, 2019
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@dominikh @gopherbot @dencoded