A Tour of Go - 第2回 dwanGo

2回目．

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
    x, y := 0, 1
    return func() int {
        x, y = y, x+y
        return x
    }
}

func main() {
    f := fibonacci()
    for i := 0; i < 10; i++ {
        fmt.Println(f())
    }
}

package main

import "fmt"
import "math/cmplx"

func Cbrt(x complex128) complex128 {
    z, z_prev := complex128(2), complex128(0)
    for ; cmplx.Abs(z-z_prev) > 1e-10; {
        z_prev = z
      z = z - (cmplx.Pow(z, 3) - x) / (3*(z*z))
    }
    return z
}

func main() {
    fmt.Println(Cbrt(2))
    fmt.Println(cmplx.Pow(Cbrt(2),3))
}

56

package main

import (
    "fmt"
    "math"
)

type ErrNegativeSqrt float64

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

func Sqrt(f float64) (float64, error) {
    if f < 0 {
        return 0, ErrNegativeSqrt(f)
    }
    z := 2.
    for i := 0; i < 10; i++ {
        z = z - (math.Pow(z, 2) - f) / (2 * z)
    }
    return z, nil
}

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

58

package main

import (
    "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.Fprint(w, s)
}

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

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

60

package main

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

type Image struct{
    Width int
    Height int
}

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

func (img *Image) Bounds() image.Rectangle {
    return image.Rect(0, 0, img.Width, img.Height)
}

func (img *Image) At(x, y int) color.Color {
    return color.RGBA{uint8(x*y), uint8(y-x), 255, 255}
}

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

61

package main

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

type rot13Reader struct {
    r io.Reader
}

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

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