Golang: Deep and Shallow Copy a Slice

2 min readNov 18, 2022

Deep copy a slice using either the built-in copy or append function to get a duplicated slice. However, assign an existed slice to a new variable gets a shallow copy whose slice header points to the same backing array as the source slice.

Table of Contents

· Deep Copy
  ∘ copy built-in function
  ∘ append built-in function
· Shallow Copy
  ∘ assignment

Deep Copy

copy built-in function

copy function copies elements from a source(src) slice into a destination(dst) slice.

func copy(dst, src []Type) int

Create a new empty slice with the same size of the src and then copy all the elements of the src to the empty slice.

Using the copy function, src and dst slices have different backing arrays. You can see the memory address of their backing array are different.

append built-in function

append function appends elements to the end of a slice.

func append(slice []Type, elems ...Type) []Type

Append all the elements of the src to an empty slice to get a duplicate slice.

Using the append function, src and dst slices have different backing arrays. You can see the memory address of their backing array are different.