Functions in Go

By: Koushik

Created: 07/29/2022 08:05

Last modified: 02/23/2025 09:54

Functions in Go are reusable blocks of code designed to perform specific tasks. They promote modularity, reusability, and cleaner program structure. A function can take zero or more parameters and can return one or more values.

Types of Function Calls

Go supports two ways to pass arguments to functions:

Call by Value: A copy of the actual parameter is passed to the function. Changes made inside the function do not affect the original variable.
Call by Reference: The reference (memory address) of the variable is passed. Any modification inside the function reflects in the original variable.

Syntax of a Function

func function_name(Parameter-list) (Return-type) {
    // function body - executable statements
}

Explanation:

func → Keyword to declare a function.
function_name → Name of the function (should be descriptive).
Parameter-list → Input values (if any).
(Return-type) → Specifies what type of value(s) the function returns.
The return type can be omitted if the function doesn’t return anything.

Example 1: Function to Add Two Numbers

package main
import "fmt"

func add(x int, y int) int {
	return x + y
}

func main() {
	fmt.Println(add(100, 200))
}

// OUTPUT: 300

Explanation:

The function add accepts two integers (x, y) and returns their sum.
Both parameters are of type int.
The fmt.Println statement prints the returned value.

Example 2: Function Returning Multiple Values

package main
import "fmt"

func swap(x, y string) (string, string) {
	return y, x
}

func main() {
	a, b := swap("Hello", "World")
	fmt.Println(a, b)
}

// OUTPUT: World Hello

Explanation:

Go supports returning multiple values from a function.
The swap function returns two strings in reversed order.

Example 3: Call by Reference (Using Pointers)

package main
import "fmt"

func updateValue(num *int) {
	*num = *num + 50
}

func main() {
	val := 100
	updateValue(&val)
	fmt.Println("Updated Value:", val)
}

// OUTPUT: Updated Value: 150

Explanation:

The function updateValue takes a pointer to an integer.
Inside the function, we dereference it (*num) to modify the actual value.
Since we passed the memory address (&val), the original variable gets updated.

Example 4: Anonymous Function

package main
import "fmt"

func main() {
	add := func(a int, b int) int {
		return a + b
	}
	fmt.Println("Sum:", add(10, 20))
}

// OUTPUT: Sum: 30

Explanation:

Anonymous functions don’t have a name.
They can be assigned to variables and used like normal functions.

Example 5: Variadic Function

package main
import "fmt"

func sum(numbers ...int) int {
	total := 0
	for _, num := range numbers {
		total += num
	}
	return total
}

func main() {
	fmt.Println(sum(1, 2, 3, 4, 5))
}

// OUTPUT: 15

Explanation: