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Variadic

Functions can take an arbitrary number of final arguments. This is done using the ... syntax in the function signature.

A variadic function receives the variadic arguments as a slice.

func concat(strs ...string) string {
    final := ""
    // strs is just a slice of strings
    for i := 0; i < len(strs); i++ {
        final += strs[i]
    }
    return final
}

func main() {
    final := concat("Hello ", "there ", "friend!")
    fmt.Println(final)
    // Output: Hello there friend!
}

The familiar fmt.Println() and fmt.Sprintf() are variadic, as are many in the standard library! fmt.Println() prints each element with space delimiters and a newline at the end.

func Println(a ...interface{}) (n int, err error)

Spread Operator

The spread operator allows us to pass a slice into a variadic function. The spread operator consists of three dots following the slice in the function call.

func printStrings(strings ...string) {
	for i := 0; i < len(strings); i++ {
		fmt.Println(strings[i])
	}
}

func main() {
    names := []string{"bob", "sue", "alice"}
    printStrings(names...)
}

Assignment

We need to sum up the costs of all individual messages so we can send an end-of-month bill to our customers.

Complete the sum function to return the sum of all inputs.

Take note of how the variadic inputs and the spread operator are used in the test suite.