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This article introduces how to copy slices in Go language.

Copying a Slice in GoLang

Copying a slice in Go can be achieved by different methods. The copy()and append()methods are commonly used for this purpose, where copy()takes a deep copy of the given slice, while append()the method copies the contents of a slice into an empty slice.

Copy a slice in Go using Copy() method

copy()method is considered as the best way to copy a slice in Golang as it creates a deep copy of the slice.

grammar:

func copy(destination, source []Type) int

The destination is the slice to copy and the source is the slice we copied from. The function returns the number of elements of the copied slice.

Code example:

package main
import "fmt"

func main() {
    // Create slices
    DemoSlice1 := []string{"Jiyik1", "Jiyik2", "Jiyik3", "Jiyik4", "Jiyik5", "Jiyik6", "Jiyik7", "Jiyik8"}
    DstSlice1 := make([]string, len(DemoSlice1))
    var DemoSlice2 []string
    DstSlice2 := []string{"Tutorials1"}
    DemoSlice3 := []string{"Jiyik9", "Jiyik10"}
    DstSlice3 := []string{"Tutorials1", "Tutorials2"}
    DemoSlice4 := []string{"Jiyik11", "Jiyik13", "Jiyik14", "Jiyik15"}
    DstSlice4 := []string{"Tutorials1", "Tutorials2", "Tutorials3"}

    // Slices Before copying
    fmt.Println("Source Slice1 is :", DemoSlice1)
    fmt.Println("Destination Slice1 is :", DstSlice1)
    fmt.Println("Source Slice2 is :", DemoSlice2)
    fmt.Println("Destination Slice2 is :", DstSlice2)
    fmt.Println("Source Slice3 is :", DemoSlice3)
    fmt.Println("Destination Slice3 is :", DstSlice3)
    fmt.Println("Source Slice4 is :", DemoSlice4)
    fmt.Println("Destination Slice1 is :", DstSlice4)

    // Copy the slices
    CopiedSlice1 := copy(DstSlice1, DemoSlice1)
    fmt.Println("\n Destination Slice 1 after copying:", DstSlice1)
    fmt.Println("Total number of elements copied:", CopiedSlice1)

    CopiedSlice2 := copy(DstSlice2, DemoSlice2)
    fmt.Println("\n Destination Slice 2 after copying:", DstSlice2)
    fmt.Println("Total number of elements copied:", CopiedSlice2)

    CopiedSlice3 := copy(DstSlice3, DemoSlice3)
    fmt.Println("\n Destination Slice 3 after copying:", DstSlice3)
    fmt.Println("Total number of elements copied:", CopiedSlice3)

    CopiedSlice4 := copy(DstSlice4, DemoSlice4)
    fmt.Println("\n Destination Slice 4 after copying:", DstSlice4)
    fmt.Println("Total number of elements copied:", CopiedSlice4)
}

The above code creates four source slices and four destination slices with different members or empty slices with the same length.

Output:

Source Slice1 is : [Jiyik1 Jiyik2 Jiyik3 Jiyik4 Jiyik5 Jiyik6 Jiyik7 Jiyik8]
Destination Slice1 is : [       ]
Source Slice2 is : []
Destination Slice2 is : [Tutorials1]
Source Slice3 is : [Jiyik9 Jiyik10]
Destination Slice3 is : [Tutorials1 Tutorials2]
Source Slice4 is : [Jiyik11 Jiyik13 Jiyik14 Jiyik15]
Destination Slice1 is : [Tutorials1 Tutorials2 Tutorials3]

 Destination Slice 1 after copying: [Jiyik1 Jiyik2 Jiyik3 Jiyik4 Jiyik5 Jiyik6 Jiyik7 Jiyik8]
Total number of elements copied: 8

 Destination Slice 2 after copying: [Tutorials1]
Total number of elements copied: 0

 Destination Slice 3 after copying: [Jiyik9 Jiyik10]
Total number of elements copied: 2

 Destination Slice 4 after copying: [Jiyik11 Jiyik13 Jiyik14]
Total number of elements copied: 3

Copying a Slice Using Append() Method in Go

appendmethod appends the contents of the given slice to the destination slice.

grammar:

func destination = append(destination, source...)

The append method copies the contents of the source slice to an empty destination slice or a slice with members. It returns a slice containing the previous members and the copied members, unlike the copy method.

Code example:

package main
import "fmt"

func main() {
    // Create slices
    DemoSlice1 := []string{"Jiyik1", "Jiyik2", "Jiyik3", "Jiyik4", "Jiyik5", "Jiyik6", "Jiyik7", "Jiyik8"}
    var DstSlice1 []string
    var DemoSlice2 []string
    DstSlice2 := []string{"Tutorials1"}
    DemoSlice3 := []string{"Jiyik9", "Jiyik10"}
    DstSlice3 := []string{"Tutorials1", "Tutorials2"}
    DemoSlice4 := []string{"Jiyik11", "Jiyik13", "Jiyik14", "Jiyik15"}
    DstSlice4 := []string{"Tutorials1", "Tutorials2", "Tutorials3"}

    // Slices Before copying
    fmt.Println("Source Slice1 is :", DemoSlice1)
    fmt.Println("Destination Slice1 is :", DstSlice1)
    fmt.Println("Source Slice2 is :", DemoSlice2)
    fmt.Println("Destination Slice2 is :", DstSlice2)
    fmt.Println("Source Slice3 is :", DemoSlice3)
    fmt.Println("Destination Slice3 is :", DstSlice3)
    fmt.Println("Source Slice4 is :", DemoSlice4)
    fmt.Println("Destination Slice1 is :", DstSlice4)

    // Copy the slices
    CopiedSlice1 := append(DstSlice1, DemoSlice1...)
    fmt.Println("The copied slice 1 after copying: ", CopiedSlice1)

    CopiedSlice2 := append(DstSlice2, DemoSlice2...)
    fmt.Println("The copied slice 2 after copying: ", CopiedSlice2)

    CopiedSlice3 := append(DstSlice3, DemoSlice3...)
    fmt.Println("The copies slice 3 after copying: ", CopiedSlice3)

    CopiedSlice4 := append(DstSlice4, DemoSlice4...)
    fmt.Println("The copied slice 4 after copying: ", CopiedSlice4)
}

The above code snippet will copy the contents of one slice to another slice.

Output:

Source Slice1 is : [Jiyik1 Jiyik2 Jiyik3 Jiyik4 Jiyik5 Jiyik6 Jiyik7 Jiyik8]
Destination Slice1 is : []
Source Slice2 is : []
Destination Slice2 is : [Tutorials1]
Source Slice3 is : [Jiyik9 Jiyik10]
Destination Slice3 is : [Tutorials1 Tutorials2]
Source Slice4 is : [Jiyik11 Jiyik13 Jiyik14 Jiyik15]
Destination Slice1 is : [Tutorials1 Tutorials2 Tutorials3]
The copied slice 1 after copying:  [Jiyik1 Jiyik2 Jiyik3 Jiyik4 Jiyik5 Jiyik6 Jiyik7 Jiyik8]
The copied slice 2 after copying:  [Tutorials1]
The copies slice 3 after copying:  [Tutorials1 Tutorials2 Jiyik9 Jiyik10]
The copied slice 4 after copying:  [Tutorials1 Tutorials2 Tutorials3 Jiyik11 Jiyik13 Jiyik14 Jiyik15]

Copying a slice using assignment method in Go

The assignment method copy is a shallow copy of the slice, we assign the source slice to the destination slice.

Code example:

package main
import "fmt"

func main() {
    // Create slices
    DemoSlice1 := []string{"Jiyik1", "Jiyik2", "Jiyik3", "Jiyik4", "Jiyik5", "Jiyik6", "Jiyik7", "Jiyik8"}
    var DemoSlice2 []string
    DemoSlice3 := []string{"Jiyik9", "Jiyik10"}
    DemoSlice4 := []string{"Jiyik11", "Jiyik13", "Jiyik14", "Jiyik15"}

    // Slices After copying
    fmt.Println("Source Slice1 is :", DemoSlice1)
    DstSlice1 := DemoSlice1
    fmt.Println("Destination Slice1 is :", DstSlice1)
    fmt.Println("Source Slice2 is :", DemoSlice2)
    DstSlice2 := DemoSlice2
    fmt.Println("Destination Slice2 is :", DstSlice2)
    fmt.Println("Source Slice3 is :", DemoSlice3)
    DstSlice3 := DemoSlice3
    fmt.Println("Destination Slice3 is :", DstSlice3)
    fmt.Println("Source Slice4 is :", DemoSlice4)
    DstSlice4 := DemoSlice4
    fmt.Println("Destination Slice1 is :", DstSlice4)
}

As we can see, we assign slices to other slices. This is a superficial approach and is not widely used because when we modify the copied content, the original slice also changes.

Output:

Source Slice1 is : [Jiyik1 Jiyik2 Jiyik3 Jiyik4 Jiyik5 Jiyik6 Jiyik7 Jiyik8]
Destination Slice1 is : [Jiyik1 Jiyik2 Jiyik3 Jiyik4 Jiyik5 Jiyik6 Jiyik7 Jiyik8]
Source Slice2 is : []
Destination Slice2 is : []
Source Slice3 is : [Jiyik9 Jiyik10]
Destination Slice3 is : [Jiyik9 Jiyik10]
Source Slice4 is : [Jiyik11 Jiyik13 Jiyik14 Jiyik15]
Destination Slice1 is : [Jiyik11 Jiyik13 Jiyik14 Jiyik15]