go一些技巧

编程语言 > golang

Created At : 2020-06-15 09:21

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go一些技巧

map第二个返回值
go语言的map有第二个返回值，能够判断在map中key是否存在
```
value, ok := kv[key]
if !ok {
 // do something
}
```
_无视其中一个值
使用_可以无视多个值中的其中几个或全部
```
_, ok := kv[key]
if !ok {
 // do something
}
```
无视全部值
```
_, _ := kv[key]
```
在切片后追加元素
```
var arr []int
arr = append(arr, 1)
```

在切片前追加元素

var arr []int
arr = append([]int{1}, arr...)

在切片后追加多个元素

var arr []int
arr = append(arr, []int{1, 2, 3, 4, 5}...)

切片越界
不会越界，是空切片

fmt.Println(arr[len(arr):])

会越界

fmt.Println(arr[len(arr)+1:])

会越界

fmt.Println(arr[len(arr)])

弃用标记

// Execer is an optional interface that may be implemented by a Conn.
//
// If a Conn does not implement Execer, the sql package's DB.Exec will
// first prepare a query, execute the statement, and then close the
// statement.
//
// Exec may return ErrSkip.
//
// Deprecated: Drivers should implement ExecerContext instead (or additionally).
type Execer interface {
 Exec(query string, args []Value) (Result, error)
}

BUG标记
```
// BUG(who): 我是bug说明
```

包注释
单独doc.go文件

package aaa
// Execer is an optional interface that may be implemented by a Conn.
//
// If a Conn does not implement Execer, the sql package's DB.Exec will
// first prepare a query, execute the statement, and then close the
// statement.
//
// Exec may return ErrSkip.

Example
文件名example_xxx_test.go
包名xxx_test
函数名func Example[FuncName][_tag]()
函数尾 // Output:

// 文件必须放在 banana包目录下, 名字必须为example_xxx_test.go
// Package banana_test 为banana包的示例
package banana_test
// 此注释将会被展示在页面上
// 此函数将被展示在OverView区域
func Example() {
fmt.Println("Hello OverView")

// Output:
// Hello OverView
}

UnitTest
文件名xxx_test.go
包名xxx_test
函数名func Test[FuncName][_tag]()

package server_test
import (
"testing"
"time"
)
func TestServerTimeLayout1(t *testing.T) {
some := time.Now().Format(types.TimeLayout1)
t.Log(some)
}

BenchmarkTest
文件名xxx_test.go
包名xxx_test
函数名func Benchmark[FuncName][_tag]()

package types_test
func BenchmarkDataMarshal(b *testing.B) {
for i := 0; i < b.N; i++ {
    data := Data{
        MsgType: DeviceReq,
        Data: []*DeviceS{
            {
                DeviceID:  "abc-123_&%S",
                ServiceID: "discrete",
                EventTime: "123456",
                Data: map[string]interface{}{
                    "LD_14.XY": "0",
                    "LD_15.XY": 0,
                    "LD_16.XY": int64(64),
                    "LD_17.XY": true,
                    "LD_18.XY": 123.456,
                },
            },
        },
    }
    _, err := json.Marshal(data)
    if err != nil {
        b.FailNow()
    }
    // fmt.Println("json", string(bytes))
}
}

交换数据

func max(a, b int) {
if a > b {
    a, b = b, a
}
}

函数返回值定义

func swap(a, b int) (max, min int) {
if a > b {
    max, min = a, b
} else {
    max, min = b, a
}
return
}

safe delete in range

m := map[string]string{
"1": "one",
"2": "two",
"3": "three",
}
for key, v := range m {
delete(m, key)
}

switch可以无参

switch {
case a == 3:
case b == 4:
case c == 7:
}

channel写数据时使用default防lock

select {
case <-quit:
case data<-event:
default:
}

无类型结构体

// Info 请求可变更字段
type Info struct {
    DNSNames []string `json:"dns"` // 证书认证dns
    Duration struct {
        Year  int `json:"year"`
        Month int `json:"month"`
        Day   int `json:"day"`
    } `json:"duration"` // 证书有效时间
    Path struct {
        Servers []struct {
            Cert string `json:"cert"`
            Key  string `json:"key"`
        } `json:"servers"`
        Clients []struct {
            Cert string `json:"cert"`
            Key  string `json:"key"`
        } `json:"clients"`
    } `json:"path"`
}

初始化与结构体声明在一起

var opts = struct {
    PrintVersion func() `short:"v" long:"version" description:"print the version of the iotx"`
    EnableDebug  func() `short:"d" long:"debug" description:"enable debug of the iotx"`
}{
    PrintVersion: func() {
        fmt.Println("Version:", Version)
        fmt.Println("BuildTime:", BuildTime)
        os.Exit(0)
    },
    EnableDebug: func() {
        logrus.SetLevel(logrus.DebugLevel)
    },
}

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