go_接口

duck typeing 

隐式的实现接口的方法就等于实现了接口

main函数

package main

import (
	"fmt"
	"learngo/retriever/mock"
	"learngo/retriever/real"
)

func main(){
	var r Retriever
	r = mock.Retriever{"this is fyf"}
	r = real.Retriever{}
	fmt.Println(download(r))
}
//interface中的函数不用加func
type Retriever interface {
	Get(url string) string
}

func download(r Retriever) string{
	return  r.Get("http://www.imooc.com")
}

　　实现接口一

package mock

type Retriever struct {
	Contents string
}

//go语言中实现了Get(url string)，就被认为实现了Retriever接口
func (r Retriever) Get(url string) string {
	return r.Contents
}

　　实现接口二（拿下慕课网首页）

package real

import (
	"time"
	"net/http"
	"net/http/httputil"
)

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)
}

Go语言里面有一个语法，可以直接判断是否是该类型的变量： value, ok= element.(T)，这里value就是变量的值，ok是一个bool类型，element是interface变量，T是断言的类型。

如果element里面确实存储了T类型的数值，那么ok返回true，否则返回false。

package main

import (
	"fmt"
	"strconv"
)

type Element interface{}
type List [] Element

type Person struct {
	name string
	age int
}

//定义了String方法，实现了fmt.Stringer
func (p Person) String() string {
	return "(name: " + p.name + " - age: "+strconv.Itoa(p.age)+ " years)"
}

func main() {
	list := make(List, 3)
	list[0] = 1 // an int
	list[1] = "Hello" // a string
	list[2] = Person{"Dennis", 70}

	for index, element := range list {
		if value, ok := element.(int); ok {
			fmt.Printf("list[%d] is an int and its value is %d
", index, value)
		} else if value, ok := element.(string); ok {
			fmt.Printf("list[%d] is a string and its value is %s
", index, value)
		} else if value, ok := element.(Person); ok {
			fmt.Printf("list[%d] is a Person and its value is %s
", index, value)
		} else {
			fmt.Println("list[%d] is of a different type", index)
		}
	}
}