How to Range Over Channel in Go: Syntax and Examples

In Go, you can use for range to receive values from a channel until it is closed. The syntax is for val := range ch, where ch is the channel. This loop automatically stops when the channel is closed.

Syntax

The syntax to range over a channel uses the for range loop. It receives values from the channel one by one until the channel is closed.

• val: variable to hold each received value
• ch: the channel to receive from
• The loop ends automatically when ch is closed

go

for val := range ch {
    // use val
}

Example

This example shows how to send integers to a channel and use for range to receive and print them until the channel is closed.

go

package main

import (
    "fmt"
)

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

    go func() {
        for i := 1; i <= 5; i++ {
            ch <- i
        }
        close(ch) // Close channel to end range loop
    }()

    for val := range ch {
        fmt.Println(val)
    }
}

Output

1
2
3
4
5

Common Pitfalls

Common mistakes when ranging over channels include:

• Not closing the channel, which causes the for range loop to block forever.
• Trying to send on a closed channel, which causes a panic.
• Using for val := range ch without a goroutine sending data, causing deadlock.

go

package main

import "fmt"

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

    // Wrong: no goroutine sending data and no close
    // for val := range ch {
    //     fmt.Println(val) // This will block forever
    // }

    // Correct way:
    go func() {
        ch <- 1
        ch <- 2
        close(ch)
    }()

    for val := range ch {
        fmt.Println(val)
    }
}

Output

1
2

Quick Reference

Tips for ranging over channels:

• Always close the channel when no more values will be sent.
• Use a goroutine to send values if the main goroutine is receiving.
• The for range loop stops automatically on channel close.

Key Takeaways

Use for val := range ch to receive values from a channel until it is closed.

Always close the channel to avoid blocking the range loop forever.

Send values on the channel from a separate goroutine to prevent deadlocks.

The range loop automatically stops when the channel is closed.

Avoid sending on a closed channel to prevent runtime panics.