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runtime: reflect string slice,the element type is interface{} #23149

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nzlov opened this issue Dec 15, 2017 · 1 comment

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@nzlov
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commented Dec 15, 2017

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

go version devel +94d7c884c3 Thu Dec 14 14:57:01 2017 +0000 darwin/amd64

Does this issue reproduce with the latest release?

YES

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/qipeng/Library/Caches/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/qipeng/workspace/go"
GORACE=""
GOROOT="/Users/qipeng/program/go"
GOTMPDIR=""
GOTOOLDIR="/Users/qipeng/program/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
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/bs/9120vpt14jd7rkhg27kdbj480000gn/T/go-build475790858=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

func main() {
    str := `
    {
        "list":[0,1,2]
    }
  `
    m := map[string]interface{}{}
    err := json.Unmarshal([]byte(str), &m)
    if err != nil {
         panic(err)
    }
    fmt.Println(reflect.ValueOf(m["list"]).Index(1).Type())
}

What did you expect to see?

int64 or float64

What did you see instead?

interface {}

@bradfitz

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commented Dec 15, 2017

This is working as intended, per the encoding/json docs:

https://golang.org/pkg/encoding/json/#Unmarshal

Which says:

[]interface{}, for JSON arrays

If you want a more specific type, you need to define a struct to unmarshal into.

@bradfitz bradfitz closed this Dec 15, 2017

@mikioh mikioh changed the title runtime:reflect string slice,the element type is interface{} runtime: reflect string slice,the element type is interface{} Jan 5, 2018

@golang golang locked and limited conversation to collaborators Jan 5, 2019

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