codewars/go/habr/two_goroutine.go

package main

import (
	"fmt"
)

// -----------------------------------------------------------------
// Работа с несколькими горутинами

func square(c chan int) {
	fmt.Println("[square] reading")
	num := <-c
	c <- num * num
}

func cube(c chan int) {
	fmt.Println("[cube] reading")
	num := <-c
	c <- num * num * num
}

func main() {
	// unidirectonalChannel()

	// anonymousGoroutine()

	channelChannel()
	/*
		fmt.Println("[main] main() started")

		squareChan := make(chan int)
		cubeChan := make(chan int)

		go square(squareChan)
		go cube(cubeChan)

		testNum := 3
		fmt.Println("[main] sent testNum to squareChan")

		squareChan <- testNum

		fmt.Println("[main] resuming")
		fmt.Println("[main] sent testNum to cubeChan")

		cubeChan <- testNum

		fmt.Println("[main] resuming")
		fmt.Println("[main] reading from channels")

		squareVal, cubeVal := <-squareChan, <-cubeChan
		sum := squareVal + cubeVal

		fmt.Println("[main] sum of square and cube of", testNum, " is", sum)
		fmt.Println("[main] main() stopped")
	*/
}

// -----------------------------------------------------------------
// Однонаправленные каналы

func greet(roc <-chan string) {
	fmt.Println("Hello " + <-roc + "!")

	// Это приведет к ошибке
	// roc <- "qwerty"
}

func unidirectonalChannel() {
	/*
		roc := make(<-chan int)
		soc := make(chan<- int)

		fmt.Printf("Data type of roc `%T`\n", roc)
		fmt.Printf("Data type of roc `%T`\n", soc)
	*/

	fmt.Println("main() started")
	c := make(chan string)

	go greet(c)

	c <- "John"
	fmt.Println("main() stopped")
}

// -----------------------------------------------------------------
// Анонимные горутины

func anonymousGoroutine() {
	fmt.Println("main() started")
	c := make(chan string)

	// launch anonymous goroutine
	go func(c chan string) {
		fmt.Println("Hello " + <-c + "!")
	}(c)

	c <- "John"
	fmt.Println("main() stopped")
}

// -----------------------------------------------------------------
// Канал с типом данных канала.
// Канал - объкт первого класса.

// gets a channels and writes a channel to it
func greeter(cc chan chan string) {
	c := make(chan string)
	cc <- c
}

func channelChannel() {
	fmt.Println("main() started")

	cc := make(chan chan string)

	go greeter(cc) // start `greeter` goroutine using `cc` channel

	c := <-cc

	go greet(c)

	c <- "John"

	fmt.Println("main() stopped")
}