About

Typically, functions accept only a fixed number of arguments. However, if you prefix the last parameter’s type with ..., the function can accept any number of trailing arguments. This makes the last parameter a variadic parameter.

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

Inside the function, the variadic parameter is a slice:

sum(1, 2, 3)    // nums is []int{1, 2, 3}
sum(1, 2, 3, 4) // nums is []int{1, 2, 3, 4}
sum()           // nums is []int{}

A function can have non-variadic parameters before the variadic one. A function can have at most one variadic parameter and it must be the last parameter.

func greet(greeting string, names ...string) {
    for _, name := range names {
        fmt.Printf("%s, %s!\n", greeting, name)
    }
}

Spreading a slice

To pass a slice into the variadic parameter, follow it with ...:

nums := []int{1, 2, 3}
sum(nums...) // equivalent to sum(1, 2, 3)

... is only valid when passing a slice to a variadic parameter.

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Originally from Exercism go concepts