Variadic Functions

// Variadic function definition (only the last parameter can be variadic).
func funcName(fixed type, args ...type) {
    // args is treated as a slice.
    for _, v := range args {
        // Process each element.
    }
}

// Calling with individual values.
funcName(fixed, value1, value2, value3)

// Expanding a slice and passing it (append ... after the slice).
slice := []int{1, 2, 3}
funcName(fixed, slice...)

package main

import "fmt"

// Variadic function that returns the sum of integers.
func sum(nums ...int) int {
    total := 0
    for _, n := range nums {
        total += n
    }
    return total
}

// Combines a fixed parameter with variadic parameters.
func logMessage(level string, messages ...string) {
    for _, msg := range messages {
        fmt.Printf("[%s] %s\n", level, msg)
    }
}

// Passes variadic arguments to another variadic function.
func printAll(args ...interface{}) {
    fmt.Println(args...) // fmt.Println itself is also variadic.
}

func main() {
    // Passing values directly.
    fmt.Println("Sum (no args):", sum())
    fmt.Println("Sum (one arg):", sum(5))
    fmt.Println("Sum (multiple):", sum(1, 2, 3, 4, 5))

    fmt.Println()

    // Expanding a slice and passing it.
    nums := []int{10, 20, 30}
    fmt.Println("From slice:", sum(nums...))

    fmt.Println()

    // Combining fixed and variadic parameters.
    logMessage("INFO", "Server started", "Listening on port 8080")
    logMessage("WARN") // Works even with no messages.

    fmt.Println()

    // Variadic with interface{}.
    printAll("Go", 42, true, 3.14)
}

Variadic functions are used throughout the standard library — fmt.Println() and fmt.Printf() both use variadic parameters internally. To forward variadic arguments to another variadic function, you must expand them with args....

If you call a variadic function with no arguments, the slice inside the function will be nil. Because len() returns 0, this is usually fine, but it is safer to perform a nil check before any slice operations such as index access.

For the basics of functions, see 'Function Definition / Multiple Return Values'. For closures, see 'Closures / Anonymous Functions'.