Golang: 面向介面
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go語言的duck typing:
- 具有python,cpp的duck typing的靈活性
- 又具有java的型別檢查
介面變數裡有什麼?
- 實現者的型別
- 實現者的值(或指標指向實現者)
注意:
- 介面變數裡自帶指標,介面變數本身採用值傳遞,幾乎不需要使用介面的指標
- 指標接收者實現只能以指標方式使用;值接收者都可以
檢視介面變數的兩種方法:
- Type Assertion
- Type Switch
golang中表示任何型別:interface{}
-
- 1.1 retriever/mock/retriever.go:
- 1.2 retriever/real/retriever.go:
- 1.3 retriever/main.go:
1
1.1 retriever/mock/retriever.go:
package mock import "fmt" type Retriever struct { Contents string } func (r *Retriever) String() string { return fmt.Sprintf( "Retriever: {Contents=%s}", r.Contents) } func (r *Retriever) Post(url string, form map[string]string) string { r.Contents = form["contents"] return "ok" } func (r *Retriever) Get(url string) string { return r.Contents }
1.2 retriever/real/retriever.go:
package real import ( "net/http" "net/http/httputil" "time" ) type Retriever struct { UserAgent string TimeOuttime.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) }
1.3 retriever/main.go:
package main import ( "fmt" "learngo/retriever/mock" "learngo/retriever/real" "time" ) // 接口裡面全是函式,不用加func關鍵字 type Retriever interface { Get(url string) string } type Poster interface { Post(url string, form map[string]string) string } const url = "http://www.imooc.com" func download(r Retriever) string { return r.Get(url) } 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) } func main() { 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) // Type assertion if mockRetriever, ok := r.(*mock.Retriever); ok { fmt.Println(mockRetriever.Contents) } else { fmt.Println("r is not a mock retriever") } fmt.Println( "Try a session with mockRetriever") fmt.Println(session(&mockRetriever)) } 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() }
1.4 Output:
Inspecting Retriever: {Contents=this is a fake imooc.com} > Type:*mock.Retriever Value:Retriever: {Contents=this is a fake imooc.com} > Type switch: Contents: this is a fake imooc.com Inspecting &{Mozilla/5.0 1m0s} > Type:*real.Retriever Value:&{Mozilla/5.0 1m0s} > Type switch: UserAgent: Mozilla/5.0 r is not a mock retriever Try a session with mockRetriever another faked imooc.com