How do you use the append function in the Go language?

2 years ago
Benjamin Taylor
2 minutes

In Go language, the append() function is used to add elements to a slice and return a new slice.

The syntax for using the append() function is as follows:

newSlice := append(slice, element1, element2, ..., elementN)

The slice is the part where elements are to be appended, and element1, element2, …, elementN are the elements to be appended.

The example code is shown below:

package main

import "fmt"

func main() {
	slice := []int{1, 2, 3}
	newSlice := append(slice, 4, 5)
	fmt.Println("Original slice:", slice)
	fmt.Println("New slice:", newSlice)
}

The output is as follows:

Original slice: [1 2 3]
New slice: [1 2 3 4 5]

The append() function can also append another slice, as shown in the example code below:

package main

import "fmt"

func main() {
	slice1 := []int{1, 2, 3}
	slice2 := []int{4, 5}
	newSlice := append(slice1, slice2...)
	fmt.Println("Original slice 1:", slice1)
	fmt.Println("Original slice 2:", slice2)
	fmt.Println("New slice:", newSlice)
}

The output is:

Original slice 1: [1 2 3]
Original slice 2: [4 5]
New slice: [1 2 3 4 5]

When using the append() function, it is important to keep the following points in mind:

  1. The append() function returns a new slice, and the original slice is not modified.
  2. If the number of elements added exceeds the capacity of the slice, the append() function will reallocate a larger underlying array, causing the original slice and the new slice to have different underlying arrays.
  3. If the number of elements added does not exceed the capacity of the slice, the append() function will append the elements on the underlying array of the original slice.
  4. If the slice being appended is an empty slice, the append() function will return the original slice.
  5. If the additional element is a slice, the slice needs to be unpacked using the … operator.
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