switch is used to make a decision based on a variable value of any type.
switch用于根据任何类型的变量值做出决定。
- Read this for more details:
Go’s switch is more general than C’s. The expressions need not be constants or even integers, the cases are evaluated top to bottom until a match is found, and if the switch has no expression it switches on true. It’s therefore possible—and idiomatic—to write an if-else-if-else chain as a switch.
Here is one example: Go Playground
Go的 switch 比C的更普遍。 表达式不必是常量甚至是整数，在找到匹配项之前从上到下评估案例， 如果switch没有表达式，则将其置为true。 因此，将if-else-if-else判断链使用switch编写是可能的，也是惯用的。
switch例子
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package main
import (
"fmt"
"runtime"
)
func main() {
fmt.Print("Go runs on ")
switch os := runtime.GOOS; os {
case "darwin":
fmt.Println("OS X.")
case "linux":
fmt.Println("Linux.")
default:
// freebsd, openbsd,
// plan9, windows...
fmt.Printf("%s.", os)
}
}
再看一个例子：
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package main
import (
"fmt"
"strconv"
)
type Element interface{}
type List []Element
type Person struct {
name string
age int
}
// 定义了String方法，实现了fmt.Stringer
func (p Person) String() string {
return "(name: " + p.name + " - age: " + strconv.Itoa(p.age) + " years)"
}
func main() {
list := make(List, 3)
list[0] = 0
list[1] = "Hello"
list[2] = Person{"Dennis", 20}
// for index, element := range list {
// if value, ok := element.(int); ok { //使用if-else-if-else 方式
// fmt.Printf("list[%d] is an int and it's value is %d\n", index, value)
// } else if value, ok := element.(string); ok {
// fmt.Printf("list[%d] is a string and it's value is %s\n", index, value)
// } else if value, ok := element.(Person); ok {
// fmt.Printf("list[%d] is a Person and it's value is %s\n", index, value)
// } else {
// fmt.Printf("list[%d] is of different type \n", index)
// }
// }
for index, element := range list {
switch value := element.(type) { //使用switch方式
case int:
fmt.Printf("list[%d] is an int and it's value is %d\n", index, value)
case string:
fmt.Printf("list[%d] is a string and it's value is %s\n", index, value)
case Person:
fmt.Printf("list[%d] is a Person and it's value is %d\n", index, value)
default:
fmt.Printf("list[%d] is of a different type\n", index)
}
}
}
The select statement lets a goroutine wait on multiple communication operations.
select语句允许goroutine等待多个通信操作。
A select blocks until one of its cases can run, then it executes that case. It chooses one at random if multiple are ready. Here is one example: Go Playground
一个select块会查找所有case直到其中一个case可以运行，然后执行该case。 如果多个case准备就绪，它会随机选择一个。 所有case都不可运行 就执行default内容。
select 例子
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package main
import (
"fmt"
"time"
)
func main() {
tick := time.Tick(100 * time.Millisecond)
boom := time.After(500 * time.Millisecond)
for {
select {
case <-tick:
fmt.Println("tick.")
case <-boom:
fmt.Println("BOOM!")
return
default:
fmt.Println(" .")
time.Sleep(50 * time.Millisecond)
}
}
}