Advance Topic

Struct

type Circle struct {
    Origin, Radius float32
}
func (c *Circle) Area() float32 {
    return math.Pi * c.Radius * c.Radius
}

Pointer

c := Circle{0.0, 1.0}
pc := &c
pc := &Circle{0.0, 1.0}

Interface

基本用法

type Task interface {
    Do() error
}
type IntTask int
func (i IntTask) Do() error {
    if i > 0 {
        return nil
    }
    return errors.New("negative int value")
}

嵌套接口

type Reader interface {
    Read(p []byte) (n int, err error)
}
type Writer interface {
    Write(p []byte) (n int, err error)
}
type ReadWriter interface {
    Reader
    Writer
}

并发

go

for i := 0; i < 4; i++ {
    go func(v int) {
        fmt.Println("v=", v)
    }(i)
}

channel

ch := make(chan int) // create a channel of type int
ch <- 42             // Send a value to the channel ch.
v := <-ch            // Receive a value from ch
// Create a buffered channel. Writing to a buffered channels does not block if less than <buffer size> unread values have been written.
ch := make(chan int, 100)
close(ch) // closes the channel (only sender should close)
// read from channel and test if it has been closed
v, ok := <-ch
// if ok is false, channel has been closed
// Read from channel until it is closed
for i := range ch {
    fmt.Println(i)
}

• 向 nil channel 发送，会阻塞

var c chan int
c <- 0
// fatal error: all goroutines are asleep - deadlock!

• 从 nil channel 读取，阻塞

var c chan int
<-c
// fatal error: all goroutines are asleep - deadlock!
// if in select, just ignore the nil channel
package main
import (
    "fmt"
    "time"
)
func main() {
    var c chan int
    d := make(chan int)
    go func() {
        select {
        case <-c:
            fmt.Println("No way")
        case <-d:
            fmt.Println("Received!")
        }
    }()
    time.Sleep(1 * time.Second)
    d <- 0
    time.Sleep(1 * time.Second)
    fmt.Println("ok")
}
// Received
// ok

• 向已关闭的 channel 发送，会 panic

c := make(chan int)
close(c)
c <- 0
// panic: send on closed channel

• 从已关闭的 channel 读取，会马上返回 0 值

var c = make(chan int, 2)
c <- 1
c <- 2
close(c)
for i := 0; i < 3; i++ {
    fmt.Printf("%d ", <-c)
}
// 1 2 0