Appending to slices in Go

Introduction

Appending to slices lets you add new items to a list that can grow as needed.

When you want to add a new item to a list of names.

When collecting user inputs one by one into a list.

When building a list of results from a loop.

When you don't know the final size of the list in advance.

Syntax

Go

slice = append(slice, newElement)

The append function returns a new slice with the element added.

You must assign the result back to the slice variable to keep the change.

Examples

Adds the number 4 to the end of the numbers slice.

Go

numbers := []int{1, 2, 3}
numbers = append(numbers, 4)

Adds the word "fun" to the words slice.

Go

words := []string{"go", "is"}
words = append(words, "fun")

Starts with an empty slice and adds 10 as the first element.

Go

var empty []int
empty = append(empty, 10)

Sample Program

This program creates a slice of fruits, adds "cherry" to it, and prints the updated slice.

Go

package main

import "fmt"

func main() {
    fruits := []string{"apple", "banana"}
    fruits = append(fruits, "cherry")
    fmt.Println(fruits)
}

Important Notes

Appending may create a new underlying array if the current one is full.

Always assign the result of append back to the slice variable.

You can append multiple elements at once: append(slice, elem1, elem2).

Summary

Use append to add elements to slices easily.

Remember to assign the result of append back to your slice.

Appending grows the slice dynamically as needed.