go channel理解不彻底遇到的问题-nil channel

代码A

package main

import (
	"fmt"
	"time"
)

func generator() chan int {
	out := make(chan int)
	go func() {
		i := 0
		for {
			//time.Sleep(time.Duration(rand.Intn(8500)) * time.Millisecond)
			time.Sleep(1 * time.Second)
			out <- i
			i++
		}
	}()
	return out
}

func worker(id int, c chan int) {
	for n := range c {
		time.Sleep(time.Second)
		fmt.Printf("Worker %d received %d\n",
			id, n)
	}
}

func createWorker(id int) chan<- int {
	c := make(chan int)
	go worker(id, c)
	return c
}

func main() {
	var c1, c2 = generator(), generator()
	var workChannel = createWorker(0)

	var values []int
	tm := time.After(10 * time.Second)
	tick := time.Tick(time.Second)
	for {
		var activeWorker chan<- int
		var activeValue int
		if len(values) > 0 {
			activeWorker = workChannel
			activeValue = values[0]
		}

		select {
		case n := <-c1:
			println("c1")
			values = append(values, n)
		case n := <-c2:
			println("c2")
			values = append(values, n)
		case activeWorker <- activeValue:
			println(activeValue)
			fmt.Println("values :", values, " activeValue:", activeValue)
			println(len(values))
			values = values[1:]

		case <-time.After(800 * time.Millisecond):
			fmt.Println("timeout")
		case <-tick:
			fmt.Println(
				"queue len =", len(values))
		case <-tm:
			fmt.Println("bye")
			return
		}
	}
}

　　代码B

package main

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

func generator() chan int {
	out := make(chan int)
	go func() {
		i := 0
		for {
			time.Sleep(time.Duration(rand.Intn(1500)) * time.Millisecond)
			//time.Sleep(1 * time.Second)
			out <- i
			i++
		}
	}()
	return out
}

func worker(id int, c chan int) {
	for n := range c {
		time.Sleep(time.Second)
		fmt.Printf("Worker %d received %d\n",
			id, n)
	}
}

func createWorker(id int) chan<- int {
	c := make(chan int)
	go worker(id, c)
	return c
}

func main() {
	var c1, c2 = generator(), generator()
	var workChannel = createWorker(0)

	var values []int
	//tm := time.After(10 * time.Second)
	tick := time.Tick(time.Second)
	for {
		// var activeWorker chan<- int
		var activeValue int
		if len(values) > 0 {
			// activeWorker = workChannel
			activeValue = values[0]
		}

		select {
		case n := <-c1:
			values = append(values, n)
		case n := <-c2:
			values = append(values, n)
		case workChannel <- activeValue:
			fmt.Println("values :", values, " activeValue:", activeValue)
			values = values[1:]
		case <-tick:
			fmt.Println(
				"queue len =", len(values))
			//case <-tm:
			//	fmt.Println("bye")
			//	return
		}
	}
}

　　代码A、B 晃眼一看基本没有什么问题，都是两个生产者一个消费者，A只是多了 activeWorker 的临时变量，中间做了转换，但是问题就出在这里，由于对于nil channel的理解不够，所以一直认为 nil channel是可以传值的，但是百思不得其解，为什么一直报错。

      网上找了教程，看了总结，才发现，原理竟然如此简单，论基础的重要性。。。。。。