Gopl 第六七章 方法与接口

发表于 | 更新于: | 分类于
字数统计: 508 字

说明

本文为GOPL第六七章学习笔记

方法

方法声明

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
type Point struct{ X, Y float64 }

type ColoredPoint struct {
	Point
	Color color.RGBA
}

func (p Point) Distance(q Point) float64 {
	dX := q.X - p.X
	dY := q.Y - p.Y
	return math.Sqrt(dX*dX + dY*dY)
}

func (p *Point) ScaleBy(factor float64) {
	p.X *= factor
	p.Y *= factor
}

func main() {
	red := color.RGBA{255, 0, 0, 255}
	blue := color.RGBA{0, 0, 255, 255}
	var p = ColoredPoint{Point{1, 1}, red}
	var q = ColoredPoint{Point{5, 4}, blue}
	fmt.Println(p.Distance(q.Point)) // "5"
	
	//p隐式转换为&p
	p.ScaleBy(2)
	q.ScaleBy(2)
	fmt.Println(p.Distance(q.Point)) // "10"

	//方法转函数
	dis := Point.Distance
	fmt.Println(dis(p.Point,q.Point)) //10
}

接口

温度转化

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
type Celsius float64
type Fahrenheit float64
type celsiusFlag struct {
	Celsius
}
type Value interface {
	String() string
	Set(string) error
}
func CToF(c Celsius) Fahrenheit { return Fahrenheit(c*9.0/5.0 + 32.0) }
func FToC(f Fahrenheit) Celsius { return Celsius((f - 32.0) * 5.0 / 9.0) }
func (f *celsiusFlag) Set(s string) error{
	var value float64
	var unit string
	fmt.Sscanf(s,"%f%s",&value,&unit)
	switch unit {
	case "C","c":
		f.Celsius = Celsius(value)
		return nil
	case "F","f":
		f.Celsius = FToC(Fahrenheit(value))
		return nil
	}
	return fmt.Errorf("invalid temperature %q",s)
}
func (c Celsius) String() string {
	return fmt.Sprintf("%.2fC",c)
}

func main(){
	var c celsiusFlag
	c.Set("34.55C")
	fmt.Println(c.Celsius)
	c.Set("100.43F")
	fmt.Println(c.Celsius)
}

http.Handler 接口

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38

package main

import (
	"fmt"
	"log"
	"net/http"
)

func main() {
	db := database{"shoes": 50, "socks": 5}
	http.HandleFunc("/list", db.list)
	http.HandleFunc("/price", db.price)
	log.Fatal(http.ListenAndServe("localhost:8000", nil))
}

type dollars float32

func (d dollars) String() string { return fmt.Sprintf("$%.2f", d) }

type database map[string]dollars

func (db database) list(w http.ResponseWriter, req *http.Request) {
	for item, price := range db {
		fmt.Fprintf(w, "%s: %s\n", item, price)
	}
}

func (db database) price(w http.ResponseWriter, req *http.Request) {
	item := req.URL.Query().Get("item")
	//localhost:8000/price?item=shoes ->  $50.00
	if price, ok := db[item]; ok {
		fmt.Fprintf(w, "%s\n", price) 
	} else {
		w.WriteHeader(http.StatusNotFound) // 404
		fmt.Fprintf(w, "no such item: %q\n", item)
	}
}