Variadic functions (...T)

• Basics
• Pass slice elements to a variadic function
• Append is variadic

Basics

If the last parameter of a function has type ...T it can be called with any number of trailing arguments of type T.

func Sum(nums ...int) int {
	res := 0
	for _, n := range nums {
		res += n
	}
	return res
}

func main()
	fmt.Println(Sum())        // 0
	fmt.Println(Sum(1, 2, 3)) // 6
}

The actual type of ...T inside the function is []T.

Pass slice elements to a variadic function

You can pass the elements of a slice s directly to a variadic function using the s... notation. In this case no new slice is created.

primes := []int{2, 3, 5, 7}
fmt.Println(Sum(primes...)) // 17

Append is variadic

The built-in append function is variadic and can be used to append any number of elements to a slice.

As a special case, you can append a string to a byte slice:

var buf []byte
buf = append(buf, 'a', 'b')
buf = append(buf, "cd"...)
fmt.Println(buf) // [97 98 99 100]

Further reading

How to append anything (element, slice or string) to a slice

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