How to pass a Slice to Function in Golang?

In Go, slices are dynamically sized arrays. They are often passed to functions when you want to manipulate or process collections of data. Slices are passed by reference, meaning that any modification made to the slice inside the function will affect the original slice outside the function.

Example

package main

import "fmt"

func printSlice(slice []int) {
    fmt.Println("Slice elements:", slice)
}

func main() {
    // Initial slice
    numbers := []int{1, 2, 3, 4, 5}

    // Passing slice to the function
    printSlice(numbers)
}

Syntax

func functionName(slice []Type) {
    // Function body                                              # Passing Slice to a Function
}

func modifySlice(slice []Type) {
    // Modify elements in the slice                               # Modify Slice Elements inside a function
}

func functionName(slice []Type, element Type) []Type {
    // Modify and return the slice                                # Returning a Slice from a Function
}

func modifySlicePointer(slice *[]Type) {
    // Modify the slice through its pointer                       # Passing a Slice to a Function with a Slice Pointer
}

Passing Slice to a function

In Go, slices are passed by reference in terms of the underlying array, meaning any modification to the elements of the slice inside a function will affect the original slice, but changes to the slice’s length or capacity will not affect the original slice outside the function.

Syntax

func functionName(slice []Type) {
    // Function body
}

Where:

• slice: The slice variable you want to pass.
• Type: The type of elements in the slice (e.g., int, string, etc.).

Example

package main
import "fmt"

func printSlice(slice []int) {
    fmt.Println("", slice)
}

func main() {
    // Initial slice
    a := []int{1, 2, 3, 4, 5}
    
    printSlice(a)
}

 [1 2 3 4 5]

Modifying Slice Elements Inside a Function

You can modify the elements of the slice inside the function, and these changes will be reflected in the original slice because slices are passed by reference.

Syntax

func modifySlice(slice []Type) {
    // Modify elements in the slice
}

Example

package main
import "fmt"

func modifySlice(slice []int) {
    for i := range slice {
        slice[i] *= 2 // Doubling each element
    }
}

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

    modifySlice(a)
    
    fmt.Println("Modified slice:", a)
}

Original slice: [1 2 3 4 5]
Modified slice: [2 4 6 8 10]

Returning a Slice from a Function

In Go, you can also return a modified slice from a function if needed.

Syntax

func functionName(slice []Type, element Type) []Type {
    // Modify and return the slice
}

Example

package main
import "fmt"

func addElement(slice []int, element int) []int {
    return append(slice, element)
}

func main() {
    // Initial slice
    a := []int{1, 2, 3}
    
    // Adding an element and returning the new slice
    newNumbers := addElement(a, 4)
    
    fmt.Println("Original slice:", a)
    fmt.Println("New slice:", newNumbers)
}

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

Passing a Slice to a Function with a Slice Pointer

While slices are already passed by reference, you can also pass a pointer to a slice if you want to modify the slice’s capacity or reassign the slice inside the function.

Syntax

func modifySlicePointer(slice *[]Type) {
    // Modify the slice through its pointer
}

Example

package main
import "fmt"

func modifySlicePointer(slice *[]int) {
    *slice = append(*slice, 6) // Adding an element using pointer
}

func main() {
    // Initial slice
    a := []int{1, 2, 3}
    fmt.Println("Original slice:", a)

    // Passing slice pointer to the function
    modifySlicePointer(&a)
    
    fmt.Println("Modified slice:", a)
}

Original slice: [1 2 3]
Modified slice: [1 2 3 6]

Conclusion

Passing slices to functions in Go is straightforward since they are reference types. You can modify the slice elements within the function, and these changes will be reflected outside the function. You can also pass a slice pointer if you need to modify the slice’s structure, such as appending to it or changing its capacity.

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Article Tags :

• Go Language
• Golang
• Golang-Slices