A Tour of Go Exercise #57-60

はじめに

こんにちは、Python界の情弱です。A Tour of Goを端からやってます。前回やってみた#43-47の演習問題に続いて、今度は#57-60をやってみます。

こんな感じ

#57 Errors

package main

import (
	"fmt"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
	return fmt.Sprintf("cannot Sqrt negative number: %f", e)
}

func Sqrt(x float64) (float64, error) {
	if x < 0 {
		return x, ErrNegativeSqrt(x)
	}
	
	z := 1.0
	delta := z
	for delta > 0.001 {
		new_z := z - (z*z - x) / 2*z
		delta = new_z - z
		z = new_z
	}
	return z, nil
}

func main() {
	fmt.Println(Sqrt(2))
	fmt.Println(Sqrt(-2))
}

#58 HTTP Handlers

package main

import (
	"fmt"
	"net/http"
)

type String string
type Struct struct {
	Greeting string
	Punct    string
	Who      string
}

func (s String) ServeHTTP(
		 w http.ResponseWriter,
		 r *http.Request) {
	fmt.Fprintf(w, string(s))
}

func (s Struct) ServeHTTP(
		 w http.ResponseWriter,
		 r *http.Request) {
	fmt.Fprintf(w, "%s %s %s", s.Greeting, s.Punct, s.Who)
}

func main() {
	// your http.Handle calls here
	http.Handle("/string", String("I'm a frayed knot."))
	http.Handle("/struct", &Struct{"Hello", ":", "Gophers!"})
	http.ListenAndServe("localhost:4000", nil)
}

#59 Image

package main

import (
	"image"
	"image/color"
	"code.google.com/p/go-tour/pic"
)

type Image struct{
	width, height int
}

func (i Image) ColorModel() color.Model {
	return color.RGBAModel
}

func (i Image) Bounds() image.Rectangle {
	return image.Rect(0, 0, i.width, i.height)
}

func (i Image) At(x, y int) color.Color {
	v := uint8((x + y) % 255)
	return color.RGBA{v, v, 255, 255}
}

func main() {
	m := Image{100, 100}
	pic.ShowImage(m)
}

#60 Rot13 Reader

package main

import (
	"io"
	"os"
	"strings"
)

type rot13Reader struct {
	r io.Reader
}

func (rr *rot13Reader) Read(p []byte) (n int, err error) {
	n, err = rr.r.Read(p)
	for i := 0; i < len(p); i++ {
		if (p[i] >= 'A' && p[i] < 'N') || (p[i] >= 'a' && p[i] < 'n') {
			p[i] += 13
		} else if (p[i] >= 'N' && p[i] <= 'Z') || (p[i] >= 'n' && p[i] <= 'z') {
			p[i] -= 13
		}
	}
	return
}

func main() {
	s := strings.NewReader(
		"Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}