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())
}
}