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)
}