golang中select和switch的区别
select
和 switch
是 Go语言中进行分支操作的两个方式,各有各的应用场景。
select
select
只能应用于channel的操作,既可以用于channel的数据接收,也可以用于channel的数据发送。
如果select
的多个分支都满足条件,则会随机的选取其中一个满足条件的分支, 如语言规范中所说:
If multiple cases can proceed, a uniform pseudo-random choice is made to decide which single communication will execute.
`case`语句的表达式可以为一个变量或者两个变量赋值。
有default
语句。
下面的代码是 go by example 上的例子:
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package main
import
"time"
import
"fmt"
func main() {
c1 :=
make(
chan
string)
c2 :=
make(
chan
string)
go
func() {
time.Sleep(time.Second *
1)
c1 <-
"one"
}()
go
func() {
time.Sleep(time.Second *
2)
c2 <-
"two"
}()
for i :=
0; i <
2; i++ {
select {
case msg1 := <-c1:
fmt.Println(
"received", msg1)
case msg2 := <-c2:
fmt.Println(
"received", msg2)
}
}
}
|
switch
switch
可以为各种类型进行分支操作, 设置可以为接口类型进行分支判断(通过i.(type))。
switch
分支是顺序执行的,这和select
不同。
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package main
import
"fmt"
import
"time"
func main() {
i :=
2
fmt.Print(
"Write ", i,
" as ")
switch i {
case
1:
fmt.Println(
"one")
case
2:
fmt.Println(
"two")
case
3:
fmt.Println(
"three")
}
switch time.Now().Weekday() {
case time.Saturday, time.Sunday:
fmt.Println(
"It's the weekend")
default:
fmt.Println(
"It's a weekday")
}
t := time.Now()
switch {
case t.Hour() <
12:
fmt.Println(
"It's before noon")
default:
fmt.Println(
"It's after noon")
}
whatAmI :=
func(i
interface{}) {
switch t := i.(
type) {
case
bool:
fmt.Println(
"I'm a bool")
case
int:
fmt.Println(
"I'm an int")
default:
fmt.Printf(
"Don't know type %T\n", t)
}
}
whatAmI(
true)
whatAmI
(1)
whatAmI(
"hey")
}
|
select
和 switch
是 Go语言中进行分支操作的两个方式,各有各的应用场景。
select
select
只能应用于channel的操作,既可以用于channel的数据接收,也可以用于channel的数据发送。
如果select
的多个分支都满足条件,则会随机的选取其中一个满足条件的分支, 如语言规范中所说:
If multiple cases can proceed, a uniform pseudo-random choice is made to decide which single communication will execute.
`case`语句的表达式可以为一个变量或者两个变量赋值。
有default
语句。
下面的代码是 go by example 上的例子:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
|
package main
import
"time"
import
"fmt"
func main() {
c1 :=
make(
chan
string)
c2 :=
make(
chan
string)
go
func() {
time.Sleep(time.Second *
1)
c1 <-
"one"
}()
go
func() {
time.Sleep(time.Second *
2)
c2 <-
"two"
}()
for i :=
0; i <
2; i++ {
select {
case msg1 := <-c1:
fmt.Println(
"received", msg1)
case msg2 := <-c2:
fmt.Println(
"received", msg2)
}
}
}
|
switch
switch
可以为各种类型进行分支操作, 设置可以为接口类型进行分支判断(通过i.(type))。
switch
分支是顺序执行的,这和select
不同。
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
|
package main
import
"fmt"
import
"time"
func main() {
i :=
2
fmt.Print(
"Write ", i,
" as ")
switch i {
case
1:
fmt.Println(
"one")
case
2:
fmt.Println(
"two")
case
3:
fmt.Println(
"three")
}
switch time.Now().Weekday() {
case time.Saturday, time.Sunday:
fmt.Println(
"It's the weekend")
default:
fmt.Println(
"It's a weekday")
}
t := time.Now()
switch {
case t.Hour() <
12:
fmt.Println(
"It's before noon")
default:
fmt.Println(
"It's after noon")
}
whatAmI :=
func(i
interface{}) {
switch t := i.(
type) {
case
bool:
fmt.Println(
"I'm a bool")
case
int:
fmt.Println(
"I'm an int")
default:
fmt.Printf(
"Don't know type %T\n", t)
}
}
whatAmI(
true)
whatAmI
(1)
whatAmI(
"hey")
}
|