BUG: value != nil returning true for nil values.

[hsblhsn]

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

$ go version
go version go1.15.6 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
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/lab44/Library/Caches/go-build"
GOENV="/Users/lab44/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/lab44/go/pkg/mod"
GOOS="darwin"
GOPATH="/Users/lab44/go"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.15.6/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.15.6/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
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/15/_y19tt655g11nh3h3b25qj100000gp/T/go-build109875245=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://play.golang.org/p/rcCFGJNhHYh

My code

package main
import (

"encoding/json"

"fmt"

"log"

"reflect"
"github.com/fatih/structs"

)
func main() {

type requestBody struct {

Title       *string

Description *string

ProductType *string

Brand       *string

}
content := []byte(`{"description": "Hello-World"}`)
var result requestBody

err := json.Unmarshal(content, &result)
if err != nil {
	log.Fatal(err)
}

fields := structs.Map(result)
updateFields := make(map[string]interface{})
for name, value := range fields {
	if value != nil {
		// no nil values should be printed here
		// Because we already checked nil values in line 31.
		// But why it's printing the value?
		//
		//
		// ORIGINAL OUTPUT:
		// Title - (*string)(nil)
		// Description - (*string)(0xc00010a140)
		// ProductType - (*string)(nil)
		// Brand - (*string)(nil)
		//
		// OUTPUT I WANT:
		// Description - (*string)(0xc00010a140)
		//
		fmt.Printf("%v - %#v\n", name, value)
		updateFields[name] = reflect.Indirect(reflect.ValueOf(value))
	}
}

}

What did you expect to see?

Description - (*string)(0xc00010a140)

What did you see instead?

Title - (*string)(nil)
Description - (*string)(0xc00010a140)
ProductType - (*string)(nil)
Brand - (*string)(nil)

[davecheney]

Thank you for this issue, this is not a bug in Go, it's a side effect of the type stored in the interface value.

There is an FAQ entry for this https://golang.org/doc/faq#nil_error (it's about errors, but applies to any interface value)

Unlike many projects, the Go project does not use GitHub Issues for general discussion or asking questions. GitHub Issues are used for tracking bugs and proposals only.

For asking questions, see:

• Stack Overflow with questions tagged "go"

• The Go Forum, a web-based forum

• Gophers Slack, use the invite app for access. The #general channel is a good starting point.

• Go Community on Hashnode with questions and posts tagged with "go"

• The golang-nuts mailing list

• IRC channel #go-nuts on Freenode

Closing as this is not a bug.

[hsblhsn]

Thank you for your response. I have fixed my issue.

In case anyone is looking for the solution:

reflect.ValueOf(value).IsNil() fixed my issue.

	fields := structs.Map(requestData)
	updateFields := make(map[string]interface{})
	for name, value := range fields {
		fieldVal := reflect.ValueOf(value)
		if !fieldVal.IsNil() {
			updateFields[name] = reflect.Indirect(fieldVal).Interface()
		}
	}

Thank you!