The Append Gotcha

The append function modifies the original slice's underlying array if there is sufficient capacity, causing changes to be visible in other slices sharing that array. To prevent this, create a new slice with a fresh underlying array using slices.Clone before appending, or manually copy the data into a new slice.

import "slices"

// Original slice
original := []int{1, 2, 3}

// Safe: Clone first to break the shared array link
copy := slices.Clone(original)

// Now append to the copy without affecting original
result := append(copy, 4)

// original remains [1, 2, 3]
// result is [1, 2, 3, 4]

In Go, a slice is just a window into a larger block of memory called an array. When you use append on a slice, it often writes directly into that shared block. If another slice is looking at the same block, it sees those changes too. To stop this, you must make a complete copy of the data into a new block of memory before you start adding to it.