How to copy one slice into another slice in Golang?

In Go, a Slice is a variable-length sequence that can hold elements of the same type. You can’t mix different types of elements in a single slice. To copy one slice into another, Go provides a built-in function called copy(). This function allows you to duplicate the elements from one slice (the source) into another slice (the destination).

Example

package  main

 import "fmt"

// Basic slice to be used in all examples
var source = []int{10, 20, 30, 40, 50}

func main() {    
fmt.Println("Source Slice:", source)
}

Syntax

func copy(dst, src []Type) int

• dst: The destination slice where elements will be copied.
• src: The source slice from which elements will be copied.
• The function returns the number of elements copied, which will be the minimum of the lengths of the source and destination slices.

Using the copy() Function

Here’s how to copy the source slice into a destination slice using the copy() function:

package main
import "fmt"

// Basic slice to be used in all examples
var source = []int{10, 20, 30, 40, 50}

func main() {
    // Creating a destination slice with the same length as the source
    destination := make([]int, len(source))
    
    // Copying the elements from source to destination
    count := copy(destination, source)
    
    // Printing the slices
    fmt.Println("Source:", source)
    fmt.Println("Destination:", destination)
    fmt.Println("Elements copied:", count)
}

Source: [10 20 30 40 50]
Destination: [10 20 30 40 50]
Elements copied: 5

Explanation

1. Creating the Slices: We create a destination slice named destination using make() that can hold the same number of elements as the source slice.
2. Copying the Elements: We use the copy() function to copy the elements from the source slice to the destination slice. The copy() function returns the number of elements that were copied.
3. Displaying the Results: Finally, we print both the source and destination slices, along with the count of elements copied.

Manual Copying with a Loop

You can copy slices manually using a loop.

Syntax

for i := 0; i < len(source); i++ {    destination[i] = source[i]}

Example:

package main
import "fmt"

// Basic slice to be used in all examples
var source = []int{10, 20, 30, 40, 50}

func main() {
    destination := make([]int, len(source))

    // Manually copying each element
    for i := 0; i < len(source); i++ {
        destination[i] = source[i]
    }

    fmt.Println("Source:", source)
    fmt.Println("Destination:", destination)
}

Source: [10 20 30 40 50]
Destination: [10 20 30 40 50]

Using a Slice Literal

If you want to create a copy of a slice while initializing it, you can use a slice literal with the append() function.

Syntax

destination = append(destination, source...)

Example:

package main
import "fmt"

// Basic slice to be used in all examples
var source = []int{10, 20, 30, 40, 50}

func main() {
    // Copying using a slice literal
    destination := []int{}
    destination = append(destination, source...)

    fmt.Println("Source:", source)
    fmt.Println("Destination:", destination)
}

Source: [10 20 30 40 50]
Destination: [10 20 30 40 50]

Note: Ensure that the destination slice is of equal or greater length than the source slice when using copy(); otherwise, the function will only copy up to the length of the destination slice.