How to Use Variadic Functions in Go: Syntax and Examples

In Go, a variadic function accepts zero or more arguments of a specified type using the syntax func name(args ...type). You can call it with any number of arguments or pass a slice with ... to expand it.

Syntax

A variadic function in Go is declared by placing ... before the type of the last parameter. This means the function can accept any number of arguments of that type.

• func: keyword to declare a function
• name: function name
• args ...type: variadic parameter that accepts zero or more values of type

Inside the function, args behaves like a slice of type.

go

func example(args ...int) {
    // args is a slice of int
}

Example

This example shows a variadic function sum that adds any number of integers and returns the total.

go

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))        // Call with 3 arguments
    fmt.Println(sum(10, 20))          // Call with 2 arguments
    nums := []int{4, 5, 6}
    fmt.Println(sum(nums...))          // Pass slice with ... to expand
}

Output

6
30
15

Common Pitfalls

Common mistakes when using variadic functions include:

• Forgetting to use ... when passing a slice to a variadic parameter.
• Trying to have multiple variadic parameters (only one is allowed and it must be last).
• Misunderstanding that inside the function, the variadic parameter is a slice.

go

package main

import "fmt"

// Wrong: multiple variadic parameters
// func wrong(a ...int, b ...string) {}

func correct(a ...int) {
    fmt.Println(a)
}

func main() {
    nums := []int{1, 2, 3}
    // Wrong: missing ... when passing slice
    // correct(nums) // This will cause a compile error

    // Right: use ... to expand slice
    correct(nums...)
}

Output

[1 2 3]

Quick Reference

Concept	Description	Example
Variadic parameter	Use ...type to accept multiple arguments	func f(nums ...int)
Call with values	Pass any number of arguments directly	f(1, 2, 3)
Call with slice	Expand slice with ...	f(slice...)
Inside function	Variadic args behave like a slice	for _, v := range nums {}
Only one variadic	Only last parameter can be variadic	No multiple ...type params

Key Takeaways

Declare variadic functions with func name(args ...type) to accept multiple arguments.

Inside the function, the variadic parameter is a slice you can loop over.

Pass a slice to a variadic function by adding ... after the slice variable.

Only one variadic parameter is allowed and it must be the last parameter.

Common errors include forgetting ... when passing slices and trying multiple variadic parameters.