go语言学习笔记

go知识归纳
- go基本概念
  - 常用基本命令
    - go build 编译包
      - 参数 -o output指定输出名称，代替默认包名
      - 参数 -i 安装相应的包，编译+go install
    - go install 安装并生成pkg、bin目录下的文件
    - go run 执行程序
    - go get 动态获取远程代码包
      - -d 只下载不安装
      - -u 强制使用网络去更新包和它的依赖包
      - -v 显示执行的命令
    - go clean
      - -i 清除关联的包和可运行的文件
      - -n 把需要执行的清除命令打印出来。
    - go fmt
      - gofmt -w -l src 格式化整个项目
    - go tool
      - go tool fix 修复以前老版本代码到新版本
      - go tool vet directory|files 分析代码是否正确例如fmt.Printf参数是否正确
  - 工作目录下结构
    - src 存放源代码，多项目可以分多个子目录
    - pkg 编译后生产的文件
    - bin 编译后生产的可执行文件

go代码规范

注释
- /** ..... **/ 注释片段、包名解释等
- // 某段说明. 开头留一个空格
常用规范
- 缩写词保持一致,例如URL
- 首字母小写: findById
- 常量首字母大写,驼峰式: MaxLength
- 错误字符串开头小写: fmt.Errorf("failed to write data")
- 声明空的slice
```
  正确:
       var t []string
  长度为0的slice:
       t := []string{}
  
```

代码规范

包名称使用单数例如model而不是models
定义包级别的错误变量

var (
     ErrCacheMiss = errors.New("memcache: cache miss")
     ErrCASConflict = errors.New("memcache: compare-and-swap conflict")
     ErrNotStored = errors.New("memcache: item not stored")
)

定义结构体

// omitempty 如果为空则忽略
type T struct {
    A bool
    B int    "myb"                     //默认0
    C string "myc,omitempty"           //默认""
    D string `bson:",omitempty" json:"jsonkey"`
}

常用构造对象方式

func NewUser(name string, age int) *User {
    return &User{
        Name: name,
        age:  age,
    }
}

代码片段

分割字符串


            str := "223,344,"
            fmt.Println(strings.Contains(str,","))
            s := strings.Split(str,",")
            for j := 0; j< len(s) ; j++  {
               fmt.Println(s[j])
            }

线程安全的整型


        type safepending struct {
            pending int
            mutex   sync.RWMutex
        }
        func (s *safepending) Inc() {
            s.mutex.Lock()
            s.pending++
            s.mutex.Unlock()
        }
        func (s *safepending) Dec() {
            s.mutex.Lock()
            s.pending--
            s.mutex.Unlock()
        }
        func (s *safepending) Get() int {
            s.mutex.RLock()
            n := s.pending
            s.mutex.RUnlock()
            return n
        }
        嵌套写法
        type safepending struct {
            pending int
            sync.RWMutex
        }
        func (s *safepending) Inc() {
            s.Lock()
            s.pending++
            s.Unlock()
        }
        func (s *safepending) Dec() {
            s.Lock()
            s.pending--
            s.Unlock()
        }
        func (s *safepending) Get() int {
            s.RLock()
            n := s.pending
            s.RUnlock()
            return n
        }

判断map值是否为空


           value, ok := myMap[myKey]
           if ok {
               //存在
           }

打印程序执行时间


           start := time.Now()
           for i := 0;i< 100000 ;i++  {
               dao.session.Ping()
           }
           end := time.Now()
           delta := end.Sub(start)
           fmt.Printf("longCalculation took this amount of time: %s\n", delta)

mongodb重连


           if err := dao.session.Ping(); err != nil {
               session.session.Refresh()
           }

重组一维数组,相同的属性为key


           result, err := db.All()
           data := make(map[string][]string)
           for _ , value := range result {
               data[value.Platform] = append(data[value.Platform], value.Version)
           }

对map数组增删改查


        // 定义map
        type MIMEHeader map[string][]string
        // Add adds the key, value pair to the header.
        // It appends to any existing values associated with key.
        func (h MIMEHeader) Add(key, value string) {
           key = CanonicalMIMEHeaderKey(key)
           h[key] = append(h[key], value)
        }
        // Set sets the header entries associated with key to
        // the single element value. It replaces any existing
        // values associated with key.
        func (h MIMEHeader) Set(key, value string) {
           h[CanonicalMIMEHeaderKey(key)] = []string{value}
        }
        // Get gets the first value associated with the given key.
        // It is case insensitive; CanonicalMIMEHeaderKey is used
        // to canonicalize the provided key.
        // If there are no values associated with the key, Get returns "".
        // To access multiple values of a key, or to use non-canonical keys,
        // access the map directly.
        func (h MIMEHeader) Get(key string) string {
           if h == nil {
               return ""
           }
           v := h[CanonicalMIMEHeaderKey(key)]
           if len(v) == 0 {
               return ""
           }
           return v[0]
        }
        // Del deletes the values associated with key.
        func (h MIMEHeader) Del(key string) {
           delete(h, CanonicalMIMEHeaderKey(key))
        }

go 结构体 omitempty


   omitempty  Only include the field if it's not set to the zero
       value for the type or to empty slices or maps.
   go 语言结构体BSON 用omitempty时要注意 为0 空数组 空map是不会更新到mongo的。

for range interface{}

          
             bool, for JSON booleans
             float64, for JSON numbers
             string, for JSON strings
             []interface{}, for JSON arrays
             map[string]interface{}, for JSON objects
             nil for JSON null
           if rec, ok := record.(map[string]interface{}); ok {
                   for key, val := range rec {
                       log.Printf(" [========>] %s = %s", key, val)
                   }
               } else {
                   fmt.Printf("record not a map[string]interface{}: %v\n", record)
               }
      </code>
  </pre>



mongodb实战


mysql实战



常用工具

包管理工具glide



性能对比

 PHP vs go

leonguo/go

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