Variadic

Sometimes a Go method must receive zero, one, or many arguments, and they can be specified directly. This is a variadic method, and it uses 3 periods in its argument list.

With variadic methods, arguments are received as a slice. But to pass a slice to a variadic method, we must use special syntax to ensure the program compiles.

Example

This Go program shows 3 functions that have variadic argument lists, and it calls the functions in a variety of ways with different arguments.

Part 1 This func receives zero, one or more string arguments, and it writes the "colors" slice with fmt.Println.

Part 2 We can receive ints (as an int slice) as well. Here we use a for-range loop to print out the integers.

Part 3 The any type means the same thing as interface{} and it refers to any type. We can use "any" in a variadic func.

Part 4 We call Example1 with direct arguments, and with a string slice (by following the slice with 3 periods).

Part 5 If we want, we can omit all arguments to a variadic method, and it will be called correctly.

Part 6 If "any" is the type of the variadic argument, we can pass various types to the method.

package main

import "fmt"

func Example1(colors ...string) {
    // Part 1: receive a string slice of any number of arguments.
    fmt.Println("Colors are", colors)
}

func Example2(values ...int) {
    // Part 2: an int slice can be received.
    fmt.Println("Values:")
    for v := range values {
        fmt.Println(v)
    }
}

func Example3(items ...any) {
    // Part 3: we can use any to mean any object like interface{}.
    fmt.Println("Items are", items)
}

func main() {
    // Part 4: call variadic method with arguments directly, and with a slice.
    Example1("blue", "red", "yellow")
    c := []string{"orange", "green"}
    Example1(c...)

    // Part 5: it is possible to use no arguments to a variadic method.
    Example2(10, 20, 30)
    Example2()

    // Part 6: for any, we can pass any values.
    Example3("bird", 10, nil)
}Colors are [blue red yellow]
Colors are [orange green]
Values:
0
1
2
Values:
Items are [bird 10 <nil>]

With variadic methods, we can receive zero, one or many arguments, and these arguments are conveniently received as a slice. A slice can be passed to a variadic method with some special syntax.