第四章 面向接口

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接口的定义

接口由使用者定义 type Retiever interface { Get( url string ) string } func download( retriever Retiever ) { return retriever.Get("http://www.baidu.com") } 接口的实现是隐式的只要实现接口里的方法

接口变量里有什么

func main() { var r Retriever ｝ // mock.go package mock type Retriever struct { Contents string } func (r *Retriever) Get(url string) string { return r.Contents } // real.go package real type Retriever struct { UserAgent string TimeOut time.Duration } func (r *Retriever) Get(url string) string { resp, err := http.Get(url) if err != nil { panic(err) } result, err := httputil.DumpResponse( resp, true) resp.Body.Close() if err != nil { panic(err) } return string(result) } 实现者的类型 和 实现者的指针接口变量自带指针接口变量才用值传递， 几乎不需要使用接口的指针

查看接口变量

表示任何类型：interface{}Type Assertion var r Retriever if mockRetriever, ok := r.(*mock.Retriever); ok { fmt.Println(mockRetriever.Contents) } else { fmt.Println("r is not a mock retriever") } Type Switch func inspect(r Retriever) { fmt.Println("Inspecting", r) fmt.Printf(" > Type:%T Value:%v\n", r, r) fmt.Print(" > Type switch: ") switch v := r.(type) { case *mock.Retriever: fmt.Println("Contents:", v.Contents) case *real.Retriever: fmt.Println("UserAgent:", v.UserAgent) } fmt.Println() } var r Retriever mockRetriever := mock.Retriever{Contents: "this is a fake imooc.com"} r = &mockRetriever inspect(r) r = &real.Retriever{ UserAgent: "Mozilla/5.0", TimeOut: time.Minute, } inspect(r)

接口的组合

type Poster interface { Post(url string, form map[string]string) string } const url = "http://www.imooc.com" func post(poster Poster) { poster.Post(url, map[string]string{ "name": "ccmouse", "course": "golang", }) } type RetrieverPoster interface { Retriever Poster } func session(s RetrieverPoster) string { s.Post(url, map[string]string{ "contents": "another faked imooc.com", }) return s.Get(url) }

特殊接口

Stringer // fmt/print.go // String() interface func (r *Retriever) String() string { return fmt.Sprintf( "Retriever: {Contents=%s}", r.Contents) } Reader/Writer func printFileContents(reader io.Reader) { scanner := bufio.NewScanner(reader) for scanner.Scan() { fmt.Println(scanner.Text()) } }