Golang中的map和闭包

Range

range可以对slice或者map进行迭代循环

package main

import "fmt"

var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}

func main() {
    for i, v := range pow {
        fmt.Printf("2**%d = %d\n", i, v)
    }
}

exercise-slices.go

package main

import "golang.org/x/tour/pic"

func Pic(dx, dy int) [][]uint8 {
    pic := make([][]uint8, dy);
    for y := range pic {
        pic[y] = make([]uint8, dx)
        for x := range pic[y] {
            pic[y][x] = uint8((x+y)/2)
        }
    }
    return pic
}

func main() {
    pic.Show(Pic)
}

map

map在使用前必须用make来创建.

package main

import "fmt"

type Vertex struct {
    Lat, Long float64
}

var m map[string]Vertex

func main() {
    m = make(map[string]Vertex)
    m["Bell Labs"] = Vertex{
        40.68433, -74.39967,
    }
    fmt.Println(m["Bell Labs"])
}

package main

import "fmt"

type Vertex struct {
    Lat, Long float64
}

var m = map[string]Vertex{
    "Bell Labs": Vertex{
        40.68433, -74.39967,
    },
    "Google": Vertex{
        37.42202, -122.08408,
    },
}

func main() {
    fmt.Println(m)
}

插入或修改一个元素：m[key] = elem

获取元素：elem = m[key]

删除元素：delete(m, key)

通过双赋值检查某个键是否存在：elem, ok = m[key] 存在ok为true

exercise-map.go

package main

import (
    "code.google.com/p/go-tour/wc"
    "strings"
)

func WordCount(s string) map[string]int {
    word_list := strings.Fields(s)
    m := make(map[string]int)
    for _, value := range word_list {
        m[value] ++
    }
    return m
}

func main() {
    wc.Test(WordCount)
}

func value

函数也可以当做值赋给变量

package main

import (
    "fmt"
    "math"
)

func main() {
    hypot := func(x, y float64) float64 {
        return math.Sqrt(x*x + y*y)
    }

    fmt.Println(hypot(3, 4))
}

闭包

package main

import "fmt"

func adder() func(int) int {
    sum := 0
    return func(x int) int {
        sum += x
        return sum
    }
}

func main() {
    pos, neg := adder(), adder()
    for i := 0; i < 10; i++ {
        fmt.Println(
            pos(i),
            neg(-2*i),
        )
    }
}

用闭包输出斐波那契数列

package main

import "fmt"

// fibonacci 函数会返回一个返回 int 的函数。
func fibonacci() func() int {
    a, b := 0, 1
    return func() int {
        a = a + b
        a, b = b, a
        return a
    }
}

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