Loops

In Go, every loop is a for loop.

C-style loops

A C-style loop has three components separated by semicolons:

• Initializer: runs once before the loop starts
• Condition: evaluated before each iteration; the loop runs while it’s true
• Post statement: runs at the end of each iteration

for i := 0; i < 5; i++ {
    // do something
}

While-style loops

Use the for keyword where other languages would use while. Omit the initializer and post statement and provide only a condition:

i := 0
for i < 5 {
    i++
}

You can also loop on any boolean condition:

for iterator.Next() {
    // do something
}

for line != lastLine {
    // do something
}

for !gotResponse || response.invalid() {
    // do something
}

Infinite loops

Omit all three components to loop forever. Infinite loops are common in servers and background workers that run until explicitly stopped:

for {
    // loop forever
}

for range

The for range loop iterates over an array, slice, map, or channel using an index and value:

for index, value := range iterable {
    // do something
}

For maps, range yields the key and value:

m := map[string]int{"a": 1, "b": 2}
for key, value := range m {
    // do something
}

If you don’t need the index, use the blank identifier:

for _, value := range iterable {
    // do something
}