Golang

【Golang】设计模式 - Generator

Posted by 西维蜀黍 on 2021-10-03, Last Modified on 2025-04-23

Generator Pattern

Channels are first-class values, just like strings or integers.

package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- fmt.Sprintf("%s %d", msg, i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return c // Return the channel to the caller.
}

func main() {
	c := boring("boring!") // Function returning a channel.
	for i := 0; i < 5; i++ {
		fmt.Printf("You say: %q\n", <-c)
	}
	fmt.Println("You're boring; I'm leaving.")
}

Channels as a handle on a service

Our boring function returns a channel that lets us communicate with the boring service it provides.

We can have more instances of the service.

func main() {
    joe := boring("Joe")
    ann := boring("Ann")
    for i := 0; i < 5; i++ {
        fmt.Println(<-joe)
        fmt.Println(<-ann)
    }
    fmt.Println("You're both boring; I'm leaving.")
}

Multiplexing

These programs make Joe and Ann count in lockstep. We can instead use a fan-in function to let whosoever is ready talk.

func fanIn(input1, input2 <-chan string) <-chan string {
    c := make(chan string)
    go func() { for { c <- <-input1 } }()
    go func() { for { c <- <-input2 } }()
    return c
}
func main() {
    c := fanIn(boring("Joe"), boring("Ann"))
    for i := 0; i < 10; i++ {
        fmt.Println(<-c)
    }
    fmt.Println("You're both boring; I'm leaving.")
}

Reference

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