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panic: runtime error: index out of range in for statement with an uint64 typed i #17940

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hyper0x opened this issue Nov 16, 2016 · 5 comments
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panic: runtime error: index out of range in for statement with an uint64 typed i #17940

hyper0x opened this issue Nov 16, 2016 · 5 comments
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@hyper0x
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hyper0x commented Nov 16, 2016 •
edited

Please answer these questions before submitting your issue. Thanks!

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

go version go1.7.3 darwin/amd64

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

GOARCH="amd64"
GOBIN="/Users/haolin/Gobin"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/haolin/Projects/gopcp.v2"
GORACE=""
GOROOT="/usr/local/go1.7"
GOTOOLDIR="/usr/local/go1.7/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/ts/7lg_tl_x2gd_k1lm5g_48c7w0000gn/T/go-build893809424=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you do?

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

https://play.golang.org/p/8EjmBiJS1h

What did you expect to see?

It run without any error.

What did you see instead?

panic: runtime error: index out of range

goroutine 1 [running]:
panic(0x90ea0, 0xc42000a0f0)
/usr/local/go1.7/src/runtime/panic.go:500 +0x1a1
main.main()
/Users/haolin/demo.go:10 +0x1c1
exit status 2

Update: That's my fault. I am sorry to interrupt. My brain was imprisoned. ;-)
@hyper0x hyper0x changed the title panic: runtime error: index out of range in for statement with a uint64 typed i panic: runtime error: index out of range in for statement with an uint64 typed i Nov 16, 2016
@0xmohit
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0xmohit commented Nov 16, 2016

The following is broken:

for i := size - 1; i >= 0; i-- {

(Note that you declared size to be an unsigned integer.)

@sathishid
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Replace the for loop with the below code to fix this usage issue.

for i := int(size) - 1; i >= 0; i--

@quentinmit
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This is not a bug.

each variable is given the type of the corresponding initialization value in the assignment

https://tip.golang.org/ref/spec#Variable_declarations

There is nothing special about assignments found in for statements. Your expression has a type because size has a type.

Except for shift operations, if one operand is an untyped constant and the other operand is not, the constant is converted to the type of the other operand.

@ianlancetaylor
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@g0hacker Let's take discussion about the language to a forum, not the issue tracker. See https://golang.org/wiki/Questions . Thanks.

@hyper0x
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hyper0x commented Nov 17, 2016

@ianlancetaylor OK, I've done: https://forum.golangbridge.org/t/why-cant-use-an-uint64-typed-variable-in-the-for-statement/3852.

@golang golang locked and limited conversation to collaborators Nov 17, 2017
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@quentinmit @hyper0x @ianlancetaylor @0xmohit @gopherbot @sathishid