关于Go,十件你可能不知道的事

1. 匿名结构体

• 全局组合

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var config struct {//定义一个用于全局配置结构体 APIKey string OAuthConfig oauth.Config } config.APIKey = "BADC0C0A"

• 数据模板

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data := struct {//匿名结构体的定义 Title string Users []*User }{//同时初始化 title, users, } err := tmpl.Execute(w, data)

(比map[string]interface{}消耗更小和更安全)

• 测试表(用作测试数据构造)

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var indexRuneTests = []struct { s string rune rune out int }{ {"a A x", 'A', 2}, {"some_text=some_value", '=', 9}, {"☺a", 'a', 3}, {"a☻☺b", '☺', 4}, }

• 嵌套加锁

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var hits struct { sync.Mutex n int } hits.Lock() hits.n++//十对“n”的操作是安全的 hits.Unlock()

2. 嵌套结构体

• 反序列化深层嵌套的json

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{"data": {"children": [ {"data": { "title": "The Go homepage", "url": "http://golang.org/" }}, ... ]}} type Item struct { Title string URL string } type Response struct { Data struct { Children []struct { Data Item } } }

3. godoc命令，输出package的文档注释

1	% godoc sync Mutex

输出

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PACKAGE package sync import "sync" TYPES type Mutex struct { // contains filtered or unexported fields } A Mutex is a mutual exclusion lock. Mutexes can be created as part of other structures; the zero value for a Mutex is an unlocked mutex. func (m *Mutex) Lock() Lock locks m. If the lock is already in use, the calling goroutine blocks until the mutex is available. func (m *Mutex) Unlock() Unlock unlocks m. It is a run-time error if m is not locked on entry to Unlock. A locked Mutex is not associated with a particular goroutine. It is allowed for one goroutine to lock a Mutex and then arrange for another goroutine to unlock it.

4. godoc -src 命令

1	% godoc -src sync Mutex

输出

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// A Mutex is a mutual exclusion lock. // Mutexes can be created as part of other structures; // the zero value for a Mutex is an unlocked mutex. type Mutex struct { state int32 sema uint32 }

未导出的元素也将显示!

5. 获取指定域名下的包

1	go get camlistore.org/pkg/netutil

go help remote 可查看更详细的信息.

6. 模拟一个文件系统

获取到的包里，代码访问了文件系统，但是测试时不希望真正访问磁盘

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var fs fileSystem = osFS{} type fileSystem interface { Open(name string) (file, error) Stat(name string) (os.FileInfo, error) } type file interface { io.Closer io.Reader io.ReaderAt io.Seeker Stat() (os.FileInfo, error) } // osFS 实现接口filesystem,并访问本地磁盘. type osFS struct{} func (osFS) Open(name string) (file, error) { return os.Open(name) } func (osFS) Stat(name string) (os.FileInfo, error) { return os.Stat(name) }

7. 方法表达式

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type T struct {} func (T) Foo(s string) { println(s) } var fn func(T, string) = T.Foo//将方法赋值给一个方法变量

os/exec中的实际例子:

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func (c *Cmd) stdin() (f *os.File, err error) func (c *Cmd) stdout() (f *os.File, err error) func (c *Cmd) stderr() (f *os.File, err error) type F func(*Cmd) (*os.File, error) for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} { fd, err := setupFd(c) if err != nil { c.closeDescriptors(c.closeAfterStart) c.closeDescriptors(c.closeAfterWait) return err } c.childFiles = append(c.childFiles, fd) }

8. 使用统一个Channel发送和接收消息

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package main import "fmt" var battle = make(chan string) func warrior(name string, done chan struct{}) { select { case opponent := <-battle: fmt.Printf("%s beat %s\n", name, opponent) case battle <- name: // I lost :-( } done <- struct{}{} } func main() { done := make(chan struct{}) langs := []string{"Go", "C", "C++", "Java", "Perl", "Python"} for _, l := range langs { go warrior(l, done) } for _ = range langs { <-done } }

9. 使用channel的close发送广播

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func waiter(i int, block, done chan struct{}) { time.Sleep(time.Duration(rand.Intn(3000)) * time.Millisecond) fmt.Println(i, "waiting...") <-block fmt.Println(i, "done!") done <- struct{}{} } func main() { block, done := make(chan struct{}), make(chan struct{}) for i := 0; i < 4; i++ { go waiter(i, block, done) } time.Sleep(5 * time.Second) close(block) for i := 0; i < 4; i++ { <-done } }

另外一个例子

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func worker(i int, ch chan Work, quit chan struct{}) { var quitting bool for { select { case w := <-ch: if quitting { w.Refuse(); fmt.Println("worker", i, "refused", w) break } w.Do(); fmt.Println("worker", i, "processed", w) case <-quit: fmt.Println("worker", i, "quitting") quitting = true } } } func main() { ch, quit := make(chan Work), make(chan struct{}) go makeWork(ch) for i := 0; i < 4; i++ { go worker(i, ch, quit) } time.Sleep(5 * time.Second) close(quit) time.Sleep(2 * time.Second) }

10. select中使用空channel

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func worker(i int, ch chan Work, quit chan struct{}) { for { select { case w := <-ch: if quit == nil { w.Refuse(); fmt.Println("worker", i, "refused", w) break } w.Do(); fmt.Println("worker", i, "processed", w) case <-quit: fmt.Println("worker", i, "quitting") quit = nil } } } func main() { ch, quit := make(chan Work), make(chan struct{}) go makeWork(ch) for i := 0; i < 4; i++ { go worker(i, ch, quit) } time.Sleep(5 * time.Second) close(quit) time.Sleep(2 * time.Second) }