go 基础学习 接口

概述

• 使用者定义接口

• 接口中包含类型和值。可以是真实的值也可以是指针，如果是真实值的化是拷贝

  • switch v := r.(type) 可以判断接口中的类型

  • (Type assertion) mockRetriever, ok := r.(*mock.Retriever)

  • 接口变量自带指针

  • 接口变量同样采用值传递，几乎不需要使用接口的指针

  • 指针接收者实现只能以指针方式使用，值接收者都可

  • 任何类型：interface{}

  • 任何类型的值强制转换 head.(int)

代码

package main
 
import (
	"fmt"
 
	"time"
 
	"golearn/retriever/mock"
	"golearn/retriever/real"
)
 
type Retriever interface {
	Get(url string) string
}
 
type Poster interface {
	Post(url string,
		form map[string]string) string
}
 
const url = "http://www.baidu.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 ctoedu.com",
	})
	return s.Get(url)
}
 
func main() {
	var r Retriever
 
	mockRetriever := mock.Retriever{
		Contents: "this is a fake ctoedu.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()
}

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
}

package real
 
import (
	"net/http"
	"net/http/httputil"
	"time"
)
 
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)
}