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Function nesting calls a function that returns a pointer that implements the error, the returned error is always not equal to nil #43767

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walkerxiong opened this issue Jan 19, 2021 · 2 comments
Closed

Function nesting calls a function that returns a pointer that implements the error, the returned error is always not equal to nil #43767

walkerxiong opened this issue Jan 19, 2021 · 2 comments
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@walkerxiong
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What version of Go are you using (go version)?

$ go version

go version go1.15.4 darwin/amd64

Does this issue reproduce with the latest release?

No

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

go env Output
$ go env
GO111MODULE="auto"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/annoymous/Library/Caches/go-build"
GOENV="/Users/annoymous/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/annoymous/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/annoymous/go"
GOPRIVATE=""
GOPROXY=""
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/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"

What did you do?

https://play.golang.org/p/DPFR2p4-7Lv

package main

import (
	"fmt"
)

type ExampleError struct {
	Code int
	Err  error
}

func (e *ExampleError) Error() string {
	return fmt.Sprintf("code[%d], %s", e.Code, e.Err)
}

func func1() error {
	return func2()
}

func func2() *ExampleError {
	return nil
}

func main() {
	if err := func1(); err != nil {
		fmt.Print("err != nil")
	}
}

What did you expect to see?

Not Print

What did you see instead?

Print err != nil
@mvdan
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mvdan commented Jan 19, 2021

The Go project doesn't use the issue tracker for questions. See https://golang.org/wiki/Questions.

@mvdan mvdan closed this as completed Jan 19, 2021
@davecheney
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This is known as a typed nil, there's an FAQ entry about this, https://golang.org/doc/faq#nil_error

@golang golang locked and limited conversation to collaborators Jan 19, 2022
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@davecheney @mvdan @gopherbot @walkerxiong