在GO语言中Slice和map都是引用类型,默认值都是nil
package main
import "fmt"
func main() {
var (
s []int
m map[int]bool
)
if s == nil {
fmt.Println("The value of s is nil")
}
if m == nil {
fmt.Println("The value of m is nil")
}
}
执行结果是:
The value of s is nil
The value of m is nil
当一个切片的值为“nil”时,是可以对它进行添加数据等操作。
package main
import "fmt"
func main() {
var s []int
fmt.Println("Is s a nil? ", s == nil)
s = append(s, 1)
fmt.Println("Is s a nil? ", s == nil)
fmt.Println(s)
}
执行结果是:
The result is like this:
Is s a nil? true
Is s a nil? false
[1]
需要注意的是当slice是nil和没有值两种状况的slice长度都是0
A caveat you should notice is the length of both nil
and empty slice is 0
:
package main
import "fmt"
func main() {
var s1 []int
s2 := []int{}
fmt.Println("Is s1 a nil? ", s1 == nil)
fmt.Println("Length of s1 is: ", len(s1))
fmt.Println("Is s2 a nil? ", s2 == nil)
fmt.Println("Length of s2 is: ", len(s2))
}
运行结果如下
The result is like this:
Is s1 a nil? true
Length of s1 is: 0
Is s2 a nil? false
Length of s2 is: 0
将slice的值与' nil '进行比较,以检查它是否是' nil '。
对一个“nil”的map取值是没有问题的,但是存储“nil”的map会引起程序panic:
package main
import "fmt"
func main() {
var m map[int]bool
fmt.Println("Is m a nil? ", m == nil)
fmt.Println("m[1] is ", m[1])
m[1] = true
}
运行结果如下
Is m a nil? true
m[1] is false
panic: assignment to entry in nil map
goroutine 1 [running]:
panic(0x4cc0e0, 0xc082034210)
C:/Go/src/runtime/panic.go:481 +0x3f4
main.main()
C:/Work/gocode/src/Hello.go:9 +0x2ee
exit status 2
Process finished with exit code 1
因此对map进行数据操作是 需要提前进行初始化,如下所示
m := make(map[int]bool)
顺便补充一点,建议使用下面的代码方式来判断map中是否存在某个键值:
if v, ok := m[1]; !ok {
.....
}
有疑问加站长微信联系(非本文作者)