1
// 声明方式1
2
var nullNameList []string
3
fmt.Println(nullNameList)
4
fmt.Println(nullNameList == nil) // true 零值问题
5
//fmt.Println(nullNameList[0]) // panic: runtime error: index out of range [0] with length 0
6

7
// 声明方式2
8
var nullClassList []string = []string{}
9
fmt.Println(nullClassList == nil) // false
10

11
// 声明方式3
12
nullClassList2 := []string{}
13
fmt.Println(nullClassList2 == nil)
14

15
// 声明方式4 （声明后再赋值）
16
nullClassList2 = make([]string, 5)
17
fmt.Println(len(nullClassList2)) // 5

1
func main() {
2
  s := []int{1, 2, 3}
3
  s1 := s[0:2] // {1,2}
4
  fmt.Println(s1)
5

6
  s1[0] = 100 // 也会将s数组下标[0]的值改为100，因为其都是指向同一底层数组
7
  fmt.Println(s)
8
  fmt.Println(s1)
9

10
  // 如需分开指向，使用copy
11
  s2 := make([]int, 3)
12
  copy(s2, s)
13
  s2[0] = 120
14
  fmt.Println(s)
15
  fmt.Println(s2)
16
}
17
------------------
18
[1 2]
19
[100 2 3]
20
[100 2]
21
[100 2 3]
22
[120 2 3]

1
// 方式1 声明Map
2
var map1 map[string]string
3
if map1 == nil {
4
  fmt.Println("map1 is nil")
5
}
6
// 分配数据空间，cap=10
7
map1 = make(map[string]string, 10)
8
fmt.Printf("map1, %T\n", map1)
9

10
// 方式2 声明Map
11
map2 := make(map[int]string)
12
map2[1] = "a"
13
map2[2] = "b"
14
map2[3] = "c"
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map2[4] = "d"
16
fmt.Printf("map2=%v\n", map2)
17

18
// 方式3
19
var userMap map[int]string = map[int]string{
20
  1: "zhangsan",
21
  2: "lisi",
22
  3: "wenwu",
23
}
24
fmt.Printf("%#v\n", userMap)

1
fmt.Println(userMap)
2
fmt.Println(userMap[1])         // zhangsan
3
fmt.Printf("%#v\n", userMap[9]) // ""
4
value1, ok := userMap[1]
5
fmt.Printf("%#v, %#v\n", value1, ok) // "zhangsan", true
6

7
value5, ok := userMap[5]
8
fmt.Printf("%#v, %#v\n", value5, ok) // "", false
9

10
// 修改value
11
userMap[1] = "Shai"
12
fmt.Printf("%#v\n", userMap[1]) // "Shai"
13

14
// 删除key
15
delete(userMap, 3)
16
fmt.Println(userMap) // map[1:Shai 2:lisi]

1
func main() {
2
  cityMap := make(map[string]string)
3

4
  // 1. 增加
5
  cityMap["China"] = "Beijing"
6
  cityMap["Japan"] = "Shanghai"
7
  cityMap["India"] = "New Delhi"
8
  fmt.Printf("cityMap=%v\n", cityMap)
9

10
  // 2. 删除
11
  delete(cityMap, "India")
12
  fmt.Printf("cityMap=%v\n", cityMap)
13

14
  // 3. 修改
15
  cityMap["Japan"] = "Tokyo"
16
  fmt.Printf("cityMap=%v\n", cityMap)
17

18
  // 4. 查询
19
  n, ok := cityMap["Japan"]
20
  fmt.Println(n, ok)
21

22
  // 5. 遍历
23
  for key, value := range cityMap {
24
    fmt.Printf("key=%v, value=%v\n", key, value)
25
  }
26

27
  // 6. 传参
28
  printMap(cityMap) // 引用传递,共同指向同一个内存地址
29
  fmt.Printf("cityMap=%v\n", cityMap)
30
}
31

32
func printMap(myMap map[string]string) {
33
  myMap["China"] = "Shanghai"
34
  myMap["England"] = "London"
35
  fmt.Printf("myMap=%v\n", myMap)
36
}
37
--------------
38
cityMap=map[China:Beijing India:New Delhi Japan:Shanghai]
39
cityMap=map[China:Beijing Japan:Shanghai]
40
cityMap=map[China:Beijing Japan:Tokyo]
41
Tokyo true
42
key=China, value=Beijing
43
key=Japan, value=Tokyo
44
myMap=map[China:Shanghai England:London Japan:Tokyo]
45
cityMap=map[China:Shanghai England:London Japan:Tokyo]