Tour of Go 2.0

Appending to a slice

To grow a slice, use the built-in append function:

func append(s []T, vs ...T) []T

You pass in a slice and one or more values, and you get back a new slice with those values added at the end.

If the underlying array is too small to fit the new values, Go allocates a bigger one automatically. The returned slice points to the new array.

You can append multiple values at once: append(s, 2, 3, 4).

Try it: Start with a nil slice and keep appending. Watch how len and cap grow.

main.go ▶ Run in Playground 
package main

import "fmt"

func main() {
	var s []int
	printSlice(s)

	// append works on nil slices.
	s = append(s, 0)
	printSlice(s)

	// The slice grows as needed.
	s = append(s, 1)
	printSlice(s)

	// We can add more than one element at a time.
	s = append(s, 2, 3, 4)
	printSlice(s)
}

func printSlice(s []int) {
	fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}