How to Insert a Value into a Go Slice at a Specific Index Without Affecting Other Elements?

Inserting a Value into a Slice at a Given Index

Question:

How can we insert a value into a specific index in a Go slice without including other elements?

Problem Description:

Suppose we have two slices, array1 and array2, and we want to insert array2[2] at array1[1]. We want to keep the rest of array1 untouched.

Background:

Earlier techniques involved using the colon operator (:), but it also includes subsequent elements. This tutorial aims to provide a comprehensive solution focused on inserting single values at a specific index.

Solution:

Using the slices.Insert Package (Go 1.21 ):

result := slices.Insert(slice, index, value)

Note: 0 ≤ index ≤ len(slice)

Using Append and Assignment

a = append(a[:index+1], a[index:]...)
a[index] = value

Note: len(a) > 0 && index < len(a)

For special cases:

• If len(a) == index, do:

  a = append(a, value)

• If inserting at index zero and dealing with an int slice, do:

  a = append([]int{value}, a...)

Custom Function:

func insert(a []int, index int, value int) []int {
    if len(a) == index {
        return append(a, value)
    }
    a = append(a[:index+1], a[index:]...)
    a[index] = value
    return a
}

Generic Function:

func insert[T any](a []T, index int, value T) []T {
    ...
    return a
}

Example:

slice1 := []int{1, 3, 4, 5}
slice2 := []int{2, 4, 6, 8}
slice1 = append(slice1[:2], slice1[1:]...)
slice1[1] = slice2[2]
fmt.Println(slice1) // [1 6 3 4 5]

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