Exercise: Loops and Functions
package main
import (
"fmt"
"math"
)
func Sqrt(x float64) float64 {
z := 1.0
for i := 1; i < 10; i++ {
z -= (z*z - x) / (2*z)
}
return z
}
func main() {
fmt.Println(Sqrt(2))
fmt.Println(math.Sqrt(2))
}Exercise: Slices
package main
import "golang.org/x/tour/pic"
func Pic(dx, dy int) [][]uint8 {
pixels := make([][]uint8, dy)
for y := 0; y < dy; y++ {
pixels[y] = make([]uint8, dx)
for x := 0; x < dx; x++ {
pixels[y][x] = uint8(x^y)
}
}
return pixels
}
func main() {
pic.Show(Pic)
}Exercise: Fibonacci closure
package main
import "fmt"
// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
a, b := -1, 1
return func() int {
a, b = b, a + b
return b
}
}
func main() {
f := fibonacci()
for i := 0; i < 10; i++ {
fmt.Println(f())
}
}Exercise: Stringers
package main
import "fmt"
type IPAddr [4]byte
func(ip IPAddr) String() string {
return fmt.Sprintf("%v.%v.%v.%v", ip[0], ip[1], ip[2], ip[3])
}
func main() {
hosts := map[string]IPAddr{
"loopback": {127, 0, 0, 1},
"googleDNS": {8, 8, 8, 8},
}
for name, ip := range hosts {
fmt.Printf("%v: %v\n", name, ip)
}
}Exercise: Errors
package main
import (
"fmt"
)
type ErrNegativeSqrt float64
func (e ErrNegativeSqrt) Error() string {
return fmt.Sprintf("cannot Sqrt negative number: %v", float64(e))
}
func Sqrt(x float64) (float64, error) {
switch {
case x < 0:
return 0, ErrNegativeSqrt(x)
default:
z := 1.0
for i := 1; i < 10; i++ {
z -= (z*z - x) / (2*z)
}
return z, nil
}
}
func main() {
fmt.Println(Sqrt(2))
fmt.Println(Sqrt(-2))
}Exercise: Readers
package main
import "golang.org/x/tour/reader"
type MyReader struct{}
func (MyReader) Read(b []byte) (n int, err error) {
b[0] = 'A';
return 1, nil;
}
func main() {
reader.Validate(MyReader{})
}Exercise: rot13Reader
package main
import (
"io"
"os"
"strings"
)
type rot13Reader struct {
r io.Reader
}
func (rot13Reader *rot13Reader) Read(bytes []byte) (int, error) {
n, err := rot13Reader.r.Read(bytes)
for i := 0; i <= n; i++ {
bytes[i] = rot13(bytes[i])
}
return n, err
}
func rot13(b byte) byte {
if 'A' <= b && b <= 'Z' {
b = b + 13
if (b > 'Z') {
return b - 26
}
}
if 'a' <= b && b <= 'z' {
b = b + 13
if (b > 'z') {
return b - 26
}
}
return b
}
func main() {
s := strings.NewReader("Lbh penpxrq gur pbqr!")
r := rot13Reader{s}
io.Copy(os.Stdout, &r)
}Exercise: Images
package main
import "image"
import "image/color"
import "golang.org/x/tour/pic"
type Image struct {
width, height int
color uint8
opacity uint8
}
func (img *Image) Bounds() image.Rectangle {
return image.Rect(0, 0, img.width, img.height)
}
func (img *Image) ColorModel() color.Model {
return color.RGBAModel
}
func (img *Image) At(x, y int) color.Color {
return color.RGBA{uint8(x^y), uint8(x^y), img.color, img.opacity}
}
func main() {
m := Image{512, 512, 255, 255}
pic.ShowImage(&m)
}Exercise: Equivalent Binary Trees
package main
import "fmt"
import "golang.org/x/tour/tree"
// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk2(t *tree.Tree, ch chan int) {
}
func Walk(t *tree.Tree, ch chan int) {
walkRecur(t, ch)
close(ch)
}
func walkRecur(t *tree.Tree, ch chan int) {
if t.Left != nil {
walkRecur(t.Left, ch)
}
ch <- t.Value
if t.Right != nil {
walkRecur(t.Right, ch)
}
}
// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
ch1, ch2 := make(chan int), make(chan int)
go Walk(t1, ch1)
go Walk(t2, ch2)
for i := range ch1 {
if i != <-ch2 {
return false
}
}
return true
}
func main() {
ch := make(chan int)
go Walk(tree.New(1), ch)
for i := range ch {
fmt.Println(i)
}
fmt.Println(Same(tree.New(1), tree.New(1)))
fmt.Println(Same(tree.New(1), tree.New(2)))
}Exercise: Web Crawler
package main
import (
"fmt"
)
type Fetcher interface {
// Fetch returns the body of URL and
// a slice of URLs found on that page.
Fetch(url string) (body string, urls []string, err error)
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, foundURLs map[string]bool) {
// TODO: Fetch URLs in parallel.
// TODO: Don't fetch the same URL twice.
// This implementation doesn't do either:
if depth <= 0 {
return
}
body, urls, err := fetcher.Fetch(url)
if err != nil {
fmt.Println(err)
foundURLs[url] = false
return
}
fmt.Printf("found: %s %q\n", url, body)
foundURLs[url] = true
for _, u := range urls {
Crawl(u, depth-1, fetcher, foundURLs)
}
return
}
func main() {
foundURLs := make(map[string]bool)
Crawl("https://golang.org/", 4, fetcher, foundURLs)
for url, success := range foundURLs {fmt.Println(url, success)}
}
// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult
type fakeResult struct {
body string
urls []string
}
func (f fakeFetcher) Fetch(url string) (string, []string, error) {
if res, ok := f[url]; ok {
return res.body, res.urls, nil
}
return "", nil, fmt.Errorf("not found: %s", url)
}
// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
"https://golang.org/": &fakeResult{
"The Go Programming Language",
[]string{
"https://golang.org/pkg/",
"https://golang.org/cmd/",
},
},
"https://golang.org/pkg/": &fakeResult{
"Packages",
[]string{
"https://golang.org/",
"https://golang.org/cmd/",
"https://golang.org/pkg/fmt/",
"https://golang.org/pkg/os/",
},
},
"https://golang.org/pkg/fmt/": &fakeResult{
"Package fmt",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
"https://golang.org/pkg/os/": &fakeResult{
"Package os",
[]string{
"https://golang.org/",
"https://golang.org/pkg/",
},
},
}参考：
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