Head First Golang

Head first Golang.

Here is the basic of go-language, including grammer basic and some features.

The content is based on the tutorial A tour of Go and I will present my understanding.

Furthermore, I will try to anaylyze the priciple

Basic

A tour of Go (Online)

Index of A tour of Go

Basic

[1] Hello world

package main
import "fmt"
func main() {
  fmt.Println("Hello, Golang World!")
}

package main
import (
  "strings"
  "golang.org/x/tour/wc"
)

func WordCount(s string) map[string]int {
  m := make(map[string]int)
  words := strings.Fields(s)
  for _, v := range words {
    m[v]++
  }
  return m
}
func main() {
  wc.Test(WordCount)
}

[9] Function As Value
- Exercise: Fibonacci closure Description
- Exercise: Fibonacci closure Solution

package main
import "fmt"
// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
  fib1 := 0
  fib2 := 1
  return func() int {
    fib2 = fib1 + fib2
    fib1 = fib2 - fib1
    return fib2 - fib1
  }
}

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

Methods and Interfaces

[1] Methods
- 注意值传递还是引用传递

package main

import "fmt"

func main() {
	/* 定义局部变量 */
	var a int = 100
	var b int = 200
	var c int = 100
	var d int = 200

	fmt.Printf("交换前 a 的值为 : %d\n", a)
	fmt.Printf("交换前 b 的值为 : %d\n", b)

	/* 通过调用函数来交换值 */
	valueSwap(a, b)

	fmt.Printf("value_swap 交换后 a 的值 : %d\n", a)
	fmt.Printf("value_swap 交换后 b 的值 : %d\n", b)

	fmt.Printf("交换前 c 的值为 : %d\n", c)
	fmt.Printf("交换前 d 的值为 : %d\n", d)

	refSwap(&c, &d)
	fmt.Printf("pref_swap 交换后 c 的值为 : %d\n", c)
	fmt.Printf("pref_swap 交换后 d 的值为 : %d\n", d)
}

/* 定义相互交换值的函数 */
func valueSwap(x, y int) int {
	var temp int

	temp = x /* 保存 x 的值 */
	x = y    /* 将 y 值赋给 x */
	y = temp /* 将 temp 值赋给 y*/

	return temp
}

/* 定义交换值函数*/
func refSwap(x *int, y *int) {
	var temp int
	temp = *x /* 保持 x 地址上的值 */
	*x = *y   /* 将 y 值赋给 x */
	*y = temp /* 将 temp 值赋给 y */
}

[2] Interfaces
- 根据函数名来确定接口实现关系

package main

import "fmt"

type Phone interface {
    call(param int) string
    takephoto()
}

type Huawei struct {
}

func (huawei Huawei) call(param int) string{
    fmt.Println("i am Huawei, i can call you!", param)
    return "damon"
}

func (huawei Huawei) takephoto() {
    fmt.Println("i can take a photo for you")
}

func main(){
    var phone Phone
    phone = new(Huawei)
    phone.takephoto()
    r := phone.call(50)
    fmt.Println(r)
}

[3] Type Assertions

package main

import "fmt"

// type switches
func do(i interface{}) {
	switch v := i.(type) {
	case int:
		fmt.Printf("Twice %v is %v\n", v, v*2)
	case string:
		fmt.Printf("%q is %v bytes long\n", v, len(v))
	default:
		fmt.Printf("I don't know about type %T!\n", v)
	}
}

func testTypeSwitchs() {
	do(21)
	do("hello")
	do(true)
}
W
func testTypeAssert() {
	var i interface{} = "hello"

	// t := i.(T)
	s := i.(string)
	fmt.Println(s)

	// f = i.(float64) // panic
	// fmt.Println(f)

	// t, ok := i.(T)
	s, ok := i.(string)
	fmt.Println(s, ok)

	f, ok := i.(float64)
	fmt.Println(f, ok)
}

func main() {
	testTypeAssert()
	testTypeSwitchs()
}

[4] Stringers

package main

import "fmt"

// Person struct
type Person struct {
	Name string
	Age  int
}

func (p Person) String() string {
	return fmt.Sprintf("%v (%v years)", p.Name, p.Age)
}

func testStringers() {
	a := Person{"Arthur Dent", 42}
	z := Person{"Zaphod Beeblebrox", 9001}
	fmt.Println(a, z)
}

// IPAddr type
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 exerciseTest() {
	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)
	}
}

func main() {
	testStringers()
	exerciseTest()
}

[5] Errors

package main

import "fmt"
func main() {
  fmt.Println("外层开始")
  defer func() {
    fmt.Println("外层准备recover")
    if err := recover(); err != nil {
      fmt.Printf("%#v-%#v\n", "外层", err) // err已经在上一级的函数中捕获了，这里没有异常，只是例行先执行defer，然后执行后面的代码
    } else {
      fmt.Println("外层没做啥事")
    }
    fmt.Println("外层完成recover")
  }()
  fmt.Println("外层即将异常")
  f()
  fmt.Println("外层异常后")
  defer func() {
    fmt.Println("外层异常后defer")
  }()
}

func f() {
  fmt.Println("内层开始")
  defer func() {
    fmt.Println("内层recover前的defer")
  }()

  defer func() {
    fmt.Println("内层准备recover")
    if err := recover(); err != nil {
      fmt.Printf("%#v-%#v\n", "内层", err) // 这里err就是panic传入的内容
    }

    fmt.Println("内层完成recover")
  }()

  defer func() {
    fmt.Println("内层异常前recover后的defer")
  }()

  panic("异常信息")

  defer func() {
    fmt.Println("内层异常后的defer")
  }()

  fmt.Println("内层异常后语句") //recover捕获的一级或者完全不捕获这里开始下面代码不会再执行
}

[6] Readers

package main

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

func basicReaderTest() {
	r := strings.NewReader("Hello, Reader!")

	b := make([]byte, 8)
	for {
		n, err := r.Read(b)
		fmt.Printf("n = %v err = %v b = %v\n", n, err, b)
		fmt.Printf("b[:n] = %q\n", b[:n])
		if err == io.EOF {
			break
		}
	}
}

// Implement a Reader type that emits an infinite stream of the ASCII character 'A'.
// import "golang.org/x/tour/reader"
// MyReader struct
type MyReader struct{}

func (r MyReader) Read(b []byte) (int, error) {
	for i := 0; i < len(b); i++ {
		b[i] = 'A'
	}
	return len(b), nil
}
func readerExercise() {
	// reader.Validate(MyReader{})
}

type rot13Reader struct {
	r io.Reader
}

func (rot *rot13Reader) Read(b []byte) (int, error) {
	n, e := rot.r.Read(b)

	for i := 0; i < n; i++ {
		if (b[i] >= 'A' && b[i] < 'N') || (b[i] >= 'a' && b[i] < 'n') {
			b[i] += 13
		} else if (b[i] > 'M' && b[i] <= 'Z') || (b[i] > 'm' && b[i] <= 'z') {
			b[i] -= 13
		}
	}
	return n, e
}

func rot13ReaderTest() {
	// Build string reader
	s := strings.NewReader("Lbh penpxrq gur pbqr!")
	// Build rot13 reader
	r := rot13Reader{s}
	// Call reader.read
	io.Copy(os.Stdout, &r)
}

func main() {
	basicReaderTest()
	rot13ReaderTest()
}

[7] Images

package main

import (
	"fmt"
	"image"
	"image/color"
	//"golang.org/x/tour/pic"
)

// package image

// type Image interface {
//     ColorModel() color.Model
//     Bounds() Rectangle
//     At(x, y int) color.Color
// }

func testImage() {
	m := image.NewRGBA(image.Rect(0, 0, 100, 100))
	fmt.Println(m.Bounds())
	fmt.Println(m.At(0, 0).RGBA())
}

// Image Struct
type Image struct{ w, h int }

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

// Bounds method
func (i Image) Bounds() image.Rectangle {
	return image.Rect(0, 0, i.w, i.h)
}

// At method
func (i Image) At(x, y int) color.Color {
	r, g, b := uint8(x*y), uint8(x^y), uint8((x+y)/2)
	return color.RGBA{r, g, b, 255}
}

func imageExercise() {
	// m := Image{1000, 1000}
	// pic.ShowImage(m)
}

func main() {
	testImage()
}

Concurrency

[1] Goroutines
- 关于 Go 的并发相关可以单独再开一篇介绍了，此处不表。

package main

import (
	"fmt"
	"time"
)

func say(s string) {
	for i := 0; i < 5; i++ {
		time.Sleep(100 * time.Millisecond)
		fmt.Println(s)
	}
}

func goroutinesTest() {
	go say("world")
	say("hello")
}

func main() {
	goroutinesTest()
}

[2] Channels
- Exercise Binary Tree Desc
- Exercise Binary Tree Solution

package main

import (
	"fmt"

	"golang.org/x/tour/tree"
)

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
	if t != nil {
		Walk(t.Left, ch)
		ch <- t.Value
		Walk(t.Right, ch)
	}
}

func goWalk(t *tree.Tree, ch chan int) {
	Walk(t, ch)
	close(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, 10), make(chan int, 10)
	go goWalk(t1, ch1)
	go goWalk(t2, ch2)
	for {
		v1, ok1 := <-ch1
		v2, ok2 := <-ch2
		if ok1 != ok2 || v1 != v2 {
			return false
		}

		if ok1 == false {
			break
		}
	}
	return true
}

func main() {
	ch := make(chan int)
	go Walk(tree.New(1), ch)
	fmt.Println(Same(tree.New(1), tree.New(2)))
	fmt.Println(Same(tree.New(1), tree.New(1)))
	fmt.Println(Same(tree.New(2), tree.New(1)))
}

[3] Mutex
- Exercise Web Crawler Desc
- Exercise Web Crawler Solution

package main

import (
	"fmt"
	// No longer needed for sleeping.
	//"time"
	"sync"
)

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)
}
type SafeCounter struct {
	v   map[string]bool
	mux sync.Mutex
	wg  sync.WaitGroup
}

var c SafeCounter = SafeCounter{v: make(map[string]bool)}

func (s SafeCounter) checkvisited(url string) bool {
	s.mux.Lock()
	defer s.mux.Unlock()
	_, ok := s.v[url]
	if ok == false {
		s.v[url] = true
		return false
	}
	return true

}

// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
	// TODO: Fetch URLs in parallel.
	// TODO: Don't fetch the same URL twice.
	// This implementation doesn't do either:
	defer c.wg.Done()
	if depth <= 0 {
		return
	}
	if c.checkvisited(url) {
		return
	}
	body, urls, err := fetcher.Fetch(url)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Printf("found: %s %q\n", url, body)
	for _, u := range urls {
		c.wg.Add(1)
		go Crawl(u, depth-1, fetcher)
	}
	return
}

func main() {
	c.wg.Add(1)
	Crawl("http://golang.org/", 4, fetcher)
	c.wg.Wait()
	// Not ideal to sleep on the main thread.
	//time.Sleep(5*time.Second)
}

// 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{
	"http://golang.org/": &fakeResult{
		"The Go Programming Language",
		[]string{
			"http://golang.org/pkg/",
			"http://golang.org/cmd/",
		},
	},
	"http://golang.org/pkg/": &fakeResult{
		"Packages",
		[]string{
			"http://golang.org/",
			"http://golang.org/cmd/",
			"http://golang.org/pkg/fmt/",
			"http://golang.org/pkg/os/",
		},
	},
	"http://golang.org/pkg/fmt/": &fakeResult{
		"Package fmt",
		[]string{
			"http://golang.org/",
			"http://golang.org/pkg/",
		},
	},
	"http://golang.org/pkg/os/": &fakeResult{
		"Package os",
		[]string{
			"http://golang.org/",
			"http://golang.org/pkg/",
		},
	},
}

Basic

Index of A tour of Go

Basic

Methods and Interfaces

Concurrency

感谢您的支持，我会继续努力的!