How to Append to Slice in Go: Simple Syntax and Examples

In Go, you append to a slice using the built-in append function like this: slice = append(slice, element). This adds the element to the end of the slice and returns the updated slice.

Syntax

The basic syntax to append an element to a slice is:

slice = append(slice, element)

Here:

• slice is your existing slice variable.
• element is the value you want to add.
• The append function returns a new slice with the element added.
• You must assign the result back to the slice variable because the underlying array may change.

go

slice = append(slice, element)

Example

This example shows how to create a slice of integers and append new numbers to it:

go

package main

import "fmt"

func main() {
    numbers := []int{1, 2, 3}
    fmt.Println("Before append:", numbers)

    numbers = append(numbers, 4)
    numbers = append(numbers, 5, 6)

    fmt.Println("After append:", numbers)
}

Output

Before append: [1 2 3]
After append: [1 2 3 4 5 6]

Common Pitfalls

One common mistake is forgetting to assign the result of append back to the slice variable. Since append may create a new underlying array, the original slice won't change if you don't assign it.

Wrong way:

slice := []int{1, 2}
append(slice, 3) // result ignored, slice unchanged
fmt.Println(slice) // prints [1 2]

Right way:

slice := []int{1, 2}
slice = append(slice, 3) // assign back
fmt.Println(slice) // prints [1 2 3]

Quick Reference

• append(slice, element): Add one element.
• append(slice, elem1, elem2, ...): Add multiple elements.
• append(slice1, slice2...): Add all elements from another slice.
• Always assign the result back to your slice variable.

Key Takeaways

Use the built-in append function to add elements to a slice in Go.

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

You can append single or multiple elements at once.

Appending may create a new underlying array, so assignment is necessary.

Appending slices requires the ... operator to unpack elements.