在通道上迭代时出现错误“范围内的变量太多”

Question

I'm kind of lost here, I was trying to get a goroutine to add to an array and another goroutine to read from it, which I suspect is somewhat close to what I have below but I need to play around with the wait().

However, I am getting the error prog.go:19:14: too many variables in range, line 19 is for _, v := range c { I can't find an answer for that online, what am I doing or not doing here?

package main

import (
    "fmt"
    //"time"
    "sync"
)

func hello(wg *sync.WaitGroup, s []int, c chan int) {
    for _, v := range s {
        c <- v
    }
    fmt.Println("Finished adding to channel")
    wg.Done()
}

func hello2(wg *sync.WaitGroup, c chan int) {
    fmt.Println("Channel",c)
    for _, v := range c {
        fmt.Println("Received",v)   
    }
    fmt.Println("Finished taking from channel")
    wg.Done()
}

func main() {
    s := []int{1, 2, 3, 4, 5}
    var c = make(chan int, 5)


    var wg sync.WaitGroup
    wg.Add(1)
    go hello(&wg, s, c)
    wg.Wait()
    wg.Add(1)
    go hello2(&wg, c)
    wg.Wait()
    //time.Sleep(1 * time.Second)
    fmt.Println("main function")
}

Answer 1

When you range over a channel, iterations only produce a single value, the values that were sent on the channel. There is no index or key value like in case of slices or maps.

So you must use:

for v := range c {
    fmt.Println("Received", v)   
}

This is detailed in Spec: For statements:

If the range expression is a channel, at most one iteration variable is permitted, otherwise there may be up to two.

And:

For channels, the iteration values produced are the successive values sent on the channel until the channel is closed. If the channel is nil, the range expression blocks forever.

And also:

Function calls on the left are evaluated once per iteration. For each iteration, iteration values are produced as follows if the respective iteration variables are present:

Range expression                          1st value          2nd value

array or slice  a  [n]E, *[n]E, or []E    index    i  int    a[i]       E
string          s  string type            index    i  int    see below  rune
map             m  map[K]V                key      k  K      m[k]       V
channel         c  chan E, <-chan E       element  e  E