接口的概念

downloader.go：

package main
import (
    "fmt"
    "imooc.com/ccmouse/learngo/infra"
    "imooc.com/ccmouse/learngo/testing"
)
func getRetriever() retriever {
    return infra.Retriever{}
    // return testing.Retriever{}
}
// 接口
type retriever interface {
    Get(string) string
}
func main() {
    var r retriever := getRetriever{}
    fmt.Println(r.Get("https://www.imooc.com"))
}

urlretriever.go：

package infra

import (
    "fmt"
    "io/ioutil"
    "net/http"
)

type Retriever struct{}

func (Retriever) Get(url string) string {
    resp, err := http.Get(url)
    if err != nil {
        panic(err)
    }

    defer resp.Body.Close()

    bytes, _ := ioutil.ReadAll(resp.Body)
    return string(bytes)

}

fakeretriever.go：

package testing

type Retriever struct{}

func (Retriever) Get(url string) string {
    return "fake content"
}