数组，切片
var a [2]string
a[0] = "Hello"
a[1] = "World"
primes := [6]int{2, 3, 5, 7, 11, 13}
// 切片（半开区间）
var s []int = primes[1:4]
names := [4]string{
"John",
"Paul",
"George",
"Ringo",
}
a := names[0:2] // [John Paul]
b := names[1:3] // [Paul George]
b[0] = "XXX" // a == [John XXX] b == [XXX George]
// 切片字面量
q := []int{2, 3, 5, 7, 11, 13}
r := []bool{true, false, true, true, false, true}
s := []struct {
i int
b bool
}{
{2, true},
{3, false},
{5, true},
{7, true},
{11, false},
{13, true},
}
// 省略上下界
s := []int{2, 3, 5, 7, 11, 13}
s = s[1:4] // [3 5 7]
s = s[:2] // [3 5]
s = s[1:] // [5]
// 长度和容量
func printSlice(s []int) {
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}
s := []int{2, 3, 5, 7, 11, 13}
printSlice(s) // len=6 cap=6 [2 3 5 7 11 13]
s = s[:0]
printSlice(s) // len=0 cap=6 []
s = s[:4]
printSlice(s) // len=4 cap=6 [2 3 5 7]
s = s[2:]
printSlice(s) // len=2 cap=4 [5 7]
// 空切片
var s []int
fmt.Println(s, len(s), cap(s)) // [] 0 0
if s == nil { // true
}
// make 函数
a := make([]int, 5)
printSlice("a", a) // a len=5 cap=5 [0 0 0 0 0]
b := make([]int, 0, 5)
printSlice("b", b) // b len=0 cap=5 []
// 切片的切片
board := [][]string{
[]string{"_", "_", "_"},
[]string{"_", "_", "_"},
[]string{"_", "_", "_"},
}
board[0][0] = "X"
board[2][2] = "O"
// append 函数
var s []int
printSlice(s) // len=0 cap=0 []
s = append(s, 0)
printSlice(s) // len=1 cap=1 [0]
s = append(s, 1)
printSlice(s) // len=2 cap=2 [0 1]
s = append(s, 2, 3, 4)
printSlice(s) // len=5 cap=6 [0 1 2 3 4]
区间
var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}
for i, v := range pow {
fmt.Printf("2**%d = %d\n", i, v)
}
/*
2**0 = 1
2**1 = 2
...
2**7 = 128
*/
for i, _ := range pow
for _, value := range pow
Map
type Vertex struct {
Lat, Long float64
}
var m map[string]Vertex
m = make(map[string]Vertex)
m["Bell Labs"] = Vertex{
40.68433, -74.39967,
}
fmt.Println(m["Bell Labs"]) // {40.68433 -74.39967}
// Map 字面量
var m = map[string]Vertex{
"Bell Labs": Vertex{
40.68433, -74.39967,
},
"Google": Vertex{
37.42202, -122.08408,
},
}
// Map 字面量
var m = map[string]Vertex{
"Bell Labs": {40.68433, -74.39967},
"Google": {37.42202, -122.08408},
}
// Map 应用
m := make(map[string]int)
m["Answer"] = 42
fmt.Println("The value:", m["Answer"]) // The value: 42
m["Answer"] = 48
fmt.Println("The value:", m["Answer"]) // The value: 48
delete(m, "Answer")
fmt.Println("The value:", m["Answer"]) // The value: 0
v, ok := m["Answer"]
fmt.Println("The value:", v, "Present?", ok) // The value: 0 Present? false
函数（高级）
// 可变参数
func myfunc(args ...int) { // args 的类型是 []int
for _, arg := range args {
fmt.Println(arg)
}
}
myfunc(2, 3, 4)
myfunc(1, 3, 7, 13)
// 函数类型
func compute(fn func(float64, float64) float64) float64 {
return fn(3, 4)
}
// 匿名函数
hypot := func(x, y float64) float64 {
return math.Sqrt(x*x + y*y)
}
fmt.Println(hypot(5, 12)) // 13
fmt.Println(compute(hypot)) // 5
fmt.Println(compute(math.Pow)) // 81
// 闭包
func adder() func(int) int {
sum := 0
return func(x int) int {
sum += x
return sum
}
}
pos, neg := adder(), adder()
for i := 0; i < 10; i++ {
fmt.Println(pos(i), neg(-2*i))
}
/*
0 0
1 -2
3 -6
6 -12
10 -20
15 -30
21 -42
28 -56
36 -72
45 -90
*/
方法
// 带接收者（receiver）的方法
type Vertex struct {
X, Y float64
}
func (v Vertex) Abs() float64 {
return math.Sqrt(v.X*v.X + v.Y*v.Y)
}
v := Vertex{3, 4}
fmt.Println(v.Abs()) // 5
// 非结构类型也可以定义方法
type MyFloat float64
func (f MyFloat) Abs() float64 {
if f < 0 {
return float64(-f)
}
return float64(f)
}
f := MyFloat(-math.Sqrt2)
fmt.Println(f.Abs()) // 1.4142135623730951
// 方法的接收者为指针
func (v *Vertex) Scale(f float64) {
v.X = v.X * f
v.Y = v.Y * f
}
v := Vertex{3, 4}
v.Scale(10)
fmt.Println(v.Abs()) // 50
// 接收者为值的方法也可以用指针来调用
// 接收者为指针的方法也可以用值来调用
var v Vertex
v.Scale(5) // OK
fmt.Println(v.Abs()) // OK
p := &v
p.Scale(10) // OK
fmt.Println(p.Abs()) // OK
// 接收者为指针的方法可以修改接收者的值
func (v *Vertex) Scale(f float64) {
v.X = v.X * f
v.Y = v.Y * f
}
// 接收者为指针的方法可以在调用时避免拷贝接收者
func (v *Vertex) Abs() float64 {
return math.Sqrt(v.X*v.X + v.Y*v.Y)
}
