golang strings.Builder type undefined - go

I was having a problem with the strings.Builder type in GO.
Attempted to run the example code verbatim and GO still responds with:
undefined: strings.Builder
Any clues as to what the problem can be, there's been not other problems at all.
package main
import (
"fmt"
"strings"
)
func main() {
var b strings.Builder
for i := 3; i >=1; i-- {
fmt.Fprintf(&b, "%x...", i)
}
b.WriteString("ignition")
fmt.Println(b.String())
}


strings.Builder was added in Go 1.10 (released 2018-02-16, 9 days ago at the time of writing). If you are building using an older version of Go, it won't be available.


If must working with older Go version, you can use bytes.Buffer instead.

Related

go testing outputs wrong case names in json format under parallel mode

go version: 1.18.1
suppose i wrote this test file parallel_test.go
package parallel_json_output
import (
"fmt"
"testing"
"time"
)
func TestP(t *testing.T) {
t.Run("a", func(t *testing.T) {
t.Parallel()
for i := 0; i < 5; i++ {
time.Sleep(time.Second)
fmt.Println("a", i)
}
})
t.Run("b", func(t *testing.T) {
t.Parallel()
for i := 0; i < 5; i++ {
time.Sleep(time.Second)
fmt.Println("b", i)
}
})
}
after running go test parallel_test.go -v -json, i got
{"Time":"2022-06-11T02:48:10.3262833+08:00","Action":"run","Package":"command-line-arguments","Test":"TestP"}
{"Time":"2022-06-11T02:48:10.3672856+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP","Output":"=== RUN TestP\n"}
{"Time":"2022-06-11T02:48:10.3682857+08:00","Action":"run","Package":"command-line-arguments","Test":"TestP/a"}
{"Time":"2022-06-11T02:48:10.3682857+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/a","Output":"=== RUN TestP/a\n"}
{"Time":"2022-06-11T02:48:10.3692857+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/a","Output":"=== PAUSE TestP/a\n"}
{"Time":"2022-06-11T02:48:10.3702858+08:00","Action":"pause","Package":"command-line-arguments","Test":"TestP/a"}
{"Time":"2022-06-11T02:48:10.3702858+08:00","Action":"run","Package":"command-line-arguments","Test":"TestP/b"}
{"Time":"2022-06-11T02:48:10.3712858+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/b","Output":"=== RUN TestP/b\n"}
{"Time":"2022-06-11T02:48:10.3712858+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/b","Output":"=== PAUSE TestP/b\n"}
{"Time":"2022-06-11T02:48:10.3722859+08:00","Action":"pause","Package":"command-line-arguments","Test":"TestP/b"}
{"Time":"2022-06-11T02:48:10.373286+08:00","Action":"cont","Package":"command-line-arguments","Test":"TestP/a"}
{"Time":"2022-06-11T02:48:10.373286+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/a","Output":"=== CONT TestP/a\n"}
{"Time":"2022-06-11T02:48:10.374286+08:00","Action":"cont","Package":"command-line-arguments","Test":"TestP/b"}
{"Time":"2022-06-11T02:48:10.374286+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/b","Output":"=== CONT TestP/b\n"}
{"Time":"2022-06-11T02:48:11.3352891+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/b","Output":"b 0\n"}
{"Time":"2022-06-11T02:48:11.3352891+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/b","Output":"a 0\n"}
...
look at this line {"Time":"2022-06-11T02:48:11.3352891+08:00","Action":"output","Package":"command-line-arguments","Test":"TestP/b","Output":"a 0\n"}. this output should be printed by case TestP/a instead of b, but the output messed up the case name in parallel tests.
this problem made reporting tool generate wrong HTML report, IDEs (like GoLand) are effected too and cannot sort parallel output correctly.
i found an issue of it in Github here, but this issue seems had been fixed already in go 1.14.6, however, it still appears in go 1.18.
i wonder what happend and how to deal with it, many thanks.

It makes sense that generic fmt package has little knowledge about currently executed tests in concurrent environment.
Testing package has its own Log method that correctly renders current test:
t.Log("a", i)

I can't import "cloud.google.com/go/datastore"

I can't understand why this :/
I tried go get -u ** with every url that I found.
Thanks
Golang:
$ go version
go version go1.13.3 windows/amd64
Source test:
package main
import (
"fmt"
"cloud.google.com/go/datastore"
)
var client *datastore.Client
func main() {
fmt.Println("Work")
}
Error:
$ go run main.go
# google.golang.org/grpc/internal/transport
..\..\..\..\google.golang.org\grpc\internal\transport\http_util.go:270:23: cannot use hf (type "vendor/golang.org/x/net/http2/hpack".HeaderField) as type
"golang.org/x/net/http2/hpack".HeaderField in argument to d.processHeaderField
..\..\..\..\google.golang.org\grpc\internal\transport\http_util.go:675:23: cannot use "golang.org/x/net/http2/hpack".NewDecoder(http2InitHeaderTableSize,
nil) (type *"golang.org/x/net/http2/hpack".Decoder) as type *"vendor/golang.org/x/net/http2/hpack".Decoder in assignment

Go requires you make use of any package that you import. In this case you are importing "cloud.google.com/go/datastore" but not doing anything with it. The global variable that you declared is also not being used. Since it seems you are just trying to test, so I would recommend you do something with it (atleast print it). Like-
package main
import (
"fmt"
"cloud.google.com/go/datastore"
)
var client *datastore.Client
func main() {
fmt.Println(client)
}

Reference to undefined identifier bytes.ReplaceAll

I am trying to build a simple webserver. I want to replace all \n with <br>.
I wanted to use bytes for this, because my page body is stored as an []byte.
I use bytes.ReplaceAll() for this. But it keeps saying that it's a reference to undefined identifier.
Can someone tell me why? I tried the exact same line within an online Compiler and it worked just fine. Do I miss the library?
See my code below:
import (
"bytes"
"html/template"
"io/ioutil"
"log"
"net/http"
"regexp"
)
type Page struct {
Title string
Body []byte
}
func editHandler(w http.ResponseWriter, r *http.Request, title string) {
p, err := loadPage(title)
if err != nil {
p = &Page{Title: title}
}
// THE LINE THAT CAUSES TROUBLE
p.Body = bytes.ReplaceAll(p.Body, []byte("\n"), []byte("<br>"))
renderTemplate(w, "edit", p)
}

The bytes package is part of the standard library, so it is unlikely that you don't have it if you have the go tool available to you.
But do note that bytes.ReplaceAll() was added in Go 1.12, so if you have an older Go SDK, this function will not be available to you.
Execute go version to find out. Get the latest Go from the official site: https://golang.org/dl/

Further to icza's answer,
For the benefit of Go versions prior to 1.12, the following are equivalent:
bytes.ReplaceAll(a, b, c)
and
bytes.Replace(a, b, c, -1)
See the implementation of ReplaceAll

Compile error when using Echo

I made a simple work using github.com/labstack/echo package while running I got this error.
github.com\labstack\echo\echo.go:624: e.AutoTLSManager.HTTPHandler
undefined (type autocert.Manager has no field or method HTTPHandler
package main
import "github.com/labstack/echo"
func main() {
e := echo.New()
e.Start(":")
}

This issue is addressed in issue #1082:
You seem to have a stale acme/autocert library. autocert.Manager DOES currently have that method: https://godoc.org/golang.org/x/crypto/acme/autocert#Manager.HTTPHandler I suggest a go get -u golang.org/x/crypto/acme/....

How to use variable package selector in go

I'm following the Go tour, and still trying to learn the basics of the language. For the imported package time, is there a way to access its exports with a variable? E.g. time[day] instead of time.Saturday
Here's a more complete example
package main
import (
"fmt"
"time"
)
func main() {
day := "Thursday"
fmt.Printf("When's %v?", day)
today := time.Now().Weekday()
switch time[day] { // This is how I would do it in javascript
case today + 0:
fmt.Println("Today.")
default:
fmt.Println("Too far away.")
}
}
Also, what is the correct terminology for what I want to do? I'm having very little luck using Google

No, there's no way to reference exported variables from a package, which are stored on the stack, without explicitly referencing them using a data structure that you define that's built at runtime.
For example, you could do:
var days = map[string]time.Weekday{
"Monday": time.Monday,
"Tuesday": time.Tuesday,
"Wednesday": time.Wednesday,
"Thursday": time.Thursday,
"Friday": time.Friday,
"Saturday": time.Saturday,
"Sunday": time.Sunday,
}
fmt.Println(days["Thursday"])
See http://play.golang.org/p/6EYqcklf8X

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