但我认为要在缓冲通道上执行范围，范围函数必须事先知道要迭代多少个元素，并且必须关闭该通道。
这种假设是错误的，是所有误解的根源。
通道范围的行为在Go Spec：https://golang.org/ref/spec#For_statements
对于通道，产生的迭代值是在通道上发送的连续值，直到通道关闭。如果通道为nil，范围表达式将永远阻塞。
在计算for语句时不需要关闭通道，并且该语句不需要知道元素的数量。
所以，在你的代码中，当你把close放在Pos 1时，这确实是正确的方法;当你把它放在Pos 3时，for循环等待通道关闭，这只能在for循环本身之后发生，所以这是一个死锁。
把close放在Pos 2中是有缺陷的，而且行为有点棘手。它 * 可能 * 引发错误，但也可能只输出两个数字。这是因为当通道在for循环之前关闭时，循环可以无阻塞地运行，然后main()返回。当main()返回时，Go程序结束，是否会引发错误完全取决于进程间的调度器是否切换到goroutine，但这并不能保证。

修改代码片段，添加一些peppered print语句到@leaf bebop的优秀答案中，以澄清发生了什么。
{1}{2}位置{3} 2 {4}，但让主电源稍等{5}{6}

func main() {
    ch := make(chan int, 2)

    go func(ch chan int) {
        for i := 1; i <= 5; i++ {
            ch <- i
            fmt.Println("Func goroutine sends data: ", i)
        }
        fmt.Println("goR work is done")
    }(ch)

    fmt.Println("Main goroutine sleeps 2 seconds")
    time.Sleep(time.Second * 2)

    fmt.Println("Main goroutine begins receiving data")
    close(ch)
    for d := range ch {
        fmt.Println("Main goroutine received data:", d)
    }

    fmt.Println("Main waiting, will the other goR panic?")
    time.Sleep(time.Second * 10)
}

Main goroutine sleeps 2 seconds
Func goroutine sends data:  1
Func goroutine sends data:  2
Main goroutine begins receiving data
Main goroutine received data: 1
panic: send on closed channel

goroutine 6 [running]:
main.main.func1(0x0?)
    /tmp/sandbox3746599466/prog.go:15 +0x3b
created by main.main
    /tmp/sandbox3746599466/prog.go:13 +0x85

Program exited.

因此，如果有足够的时间（主例程没有退出），调度程序返回到go例程，在那里我们写入一个关闭的（由主例程关闭的）通道- Panic！

位置2，但仅发送2个值，即不写入关闭的通道

func main() {
    ch := make(chan int, 2)

    go func(ch chan int) {
        // Send only 2 values
        for i := 1; i <= 2; i++ {
            ch <- i
            fmt.Println("Func goroutine sends data: ", i)
        }
        fmt.Println("goR work is done")
    }(ch)

    fmt.Println("Main goroutine sleeps 2 seconds")
    time.Sleep(time.Second * 2)

    fmt.Println("Main goroutine begins receiving data")
    close(ch)
    for d := range ch {
        fmt.Println("Main goroutine received data:", d)
    }

    fmt.Println("Main waiting, will the other goR panic?")
    time.Sleep(time.Second * 10)
    fmt.Println("Main exiting")
}

Main goroutine sleeps 2 seconds
Func goroutine sends data:  1
Func goroutine sends data:  2
goR work is done
Main goroutine begins receiving data
Main goroutine received data: 1
Main goroutine received data: 2
Main waiting, will the other goR panic?
Main exiting

Program exited.

没有恐慌，永远没有旋转。主程序只是退出。
{1}{2}位置{3} 3 {4}，检查总管是否畅通？{5}{6}

func main() {
    ch := make(chan int, 2)

    go func(ch chan int) {
        for i := 1; i <= 5; i++ {
            ch <- i
            fmt.Println("Func goroutine sends data: ", i)

        }
        fmt.Println("Routine done with work")
    }(ch)

    fmt.Println("Main goroutine sleeps 2 seconds")
    time.Sleep(time.Second * 2)

    fmt.Println("Main goroutine begins receiving data")
    for d := range ch {
        fmt.Println("Main goroutine received data:", d)
    }

    fmt.Println("Have I closed this channel?")
    close(ch)
    fmt.Println("I have")
}

Main goroutine sleeps 2 seconds
Func goroutine sends data:  1
Func goroutine sends data:  2
Main goroutine begins receiving data
Main goroutine received data: 1
Main goroutine received data: 2
Main goroutine received data: 3
Func goroutine sends data:  3
Func goroutine sends data:  4
Func goroutine sends data:  5
Routine done with work
Main goroutine received data: 4
Main goroutine received data: 5
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [chan receive]:
main.main()
    /tmp/sandbox3301646152/prog.go:26 +0x194

Program exited.

Main甚至没有关闭通道，它在range循环中被阻塞了。它将永远停留在这里，直到它得到一个值，或者有人关闭了通道。我们没有任何其他例程来做这件事，所以死锁。