communication with channels of type array

I'm trying using a simple model here to test my understanding of go channels. in the small snippet below I try to use 2 processes of a fake news feed that append several headlines to a local array then pass that to the array string channel. in main I pass these array back to a different process for printing.

Edit: I forgot to mention the problem.. my issue is that I keep getting 'index out of boundary' exception and I'm unable to compile the code.

Now I tried this same code with plain string variables and it works.

string array code:

package main
import (
"fmt"
"math/rand"
"time"
)
func main() {
/* initialization and assignment of channels */
c := make(chan []string)
p := make(chan []string)
/* Pass created channels to Goroutines */
go Feeder1(p)
go Feeder2(p)
go Consumer(c)
for {
select {
case produced := <-p:
c <- produced
/*case <-time.After(6 * time.Second):
return*/
default:
fmt.Printf("\n --- We timed out! --- \n")
time.Sleep(5 * time.Second)
}
}
}
func Feeder2(w chan []string) {
headlines := []string{
"BBC: Speedboat victim 'doted on family'\n",
"BBC: Syria rebel sarin claim downplayed\n",
"BBC: German 'ex-Auschwitz guard' arrested\n",
"BBC: Armless artist 'denied entry' to UK\n",
"BBC: Bangladesh protest clashes kill 27\n",
"BBC: Ex-Italian PM Giulio Andreotti dies\n"}
for i := 0; ; i++ {
selection := []string{}
for s := 0; s <= 3; s++ {
selection
展开收缩
 = headlines[randInt(0, len(headlines))]
}
w <- selection
time.Sleep(5 * time.Second)
}
}
func Feeder1(w chan []string) {
headlines := []string{
"SKY: Deadly Virus Can 'Spread Between People'\n",
"SKY: Ariel Castro's Brothers Brand Him 'A Monster'\n",
"SKY: Astronaut Ends Space Mission With Bowie Song\n",
"SKY: Chinese Artist Films Violent Street Brawl\n",
"SKY: May Washout: Fortnight's Rainfall In One Day\n",
"SKY: Mother's Day Shooting: CCTV Shows Suspect\n"}
for i := 0; ; i++ {
selection := []string{}
for q := 0; q <= 3; q++ {
selection[q] = headlines[randInt(0, len(headlines))]
}
w <- selection
//randomTimeValue := randInt(5, 6)
time.Sleep(2 * time.Second)
}
}
func Consumer(n chan []string) {
for {
v := <-n
for _, x := range v {
fmt.Printf("Headline:\t%s", x)
}
}
}
func randInt(min int, max int) int {
return min + rand.Intn(max-min)
}

The previously running version of the code (no arrays here):

package main
import (
"fmt"
"math/rand"
"time"
)
func main() {
/* initialization and assignment of channels */
c := make(chan string)
p := make(chan string)
/* Pass created channels to Goroutines */
go Feeder1(p)
go Feeder2(p)
go Consumer(c)
for {
select {
case produced := <-p:
c <- produced
/*case <-time.After(6 * time.Second):
return*/
default:
fmt.Printf("\n --- We timed out! --- \n")
time.Sleep(5 * time.Second)
}
}
}
func Feeder2(w chan string) {
headlines := []string{
"BBC: Speedboat victim 'doted on family'\n",
"BBC: Syria rebel sarin claim downplayed\n",
"BBC: German 'ex-Auschwitz guard' arrested\n",
"BBC: Armless artist 'denied entry' to UK\n",
"BBC: Bangladesh protest clashes kill 27\n",
"BBC: Ex-Italian PM Giulio Andreotti dies\n"}
for i := 0; ; i++ {
w <- headlines[randInt(0, len(headlines))]
time.Sleep(5 * time.Second)
}
}
func Feeder1(w chan string) {
headlines := []string{
"SKY: Deadly Virus Can 'Spread Between People'\n",
"SKY: Ariel Castro's Brothers Brand Him 'A Monster'\n",
"SKY: Astronaut Ends Space Mission With Bowie Song\n",
"SKY: Chinese Artist Films Violent Street Brawl\n",
"SKY: May Washout: Fortnight's Rainfall In One Day\n",
"SKY: Mother's Day Shooting: CCTV Shows Suspect\n"}
for i := 0; ; i++ {
w <- headlines[randInt(0, len(headlines))]
//randomTimeValue := randInt(5, 6)
time.Sleep(2 * time.Second)
}
}
func Consumer(n chan string) {
for {
v := <-n
fmt.Printf("Headline:\t%s", v)
}
}
func randInt(min int, max int) int {
return min + rand.Intn(max-min)
}

Both of these versions wont work on playground website.

Thank you

Your problem is here:

selection := []string{}
for s := 0; s <= 3; s++ {
selection
展开收缩
 = headlines[randInt(0, len(headlines))]
}

selection is a slice of length 0. When you try to set values to indexes 0, 1 and 2 - that's causing a runtime error because there's no space allocated for them.

The preferred way to initialize a slice is using make():

selection := make([]string, 3, 3)
for s := 0; s <= 3; s++ {
selection
展开收缩
 = headlines[randInt(0, len(headlines))]
}

The third argument to make() is capacity.

Another possibility is to let the runtime grow your slice implicitly by using append():

selection := []string{}
for s := 0; s <= 3; s++ {
selection = append(selection, headlines[randInt(0, len(headlines))])
}

append() will grow a slice as necessary.

Link to relevant documentation

Your string "array" code is using slices, not arrays.
You are doing selection[q] = something, but your slice
has length 0, that should panic. Either: Make proper
slice with len != 0 or do use an array.

(I personally prefer playground code).