Variadic parameters in Swift Closure

Definition

A variadic parameter accepts zero or more values of a specified type. You use a variadic parameter to specify that the parameter can be passed a varying number of input values when the closure is called.

Variadic parameters can be used in closures only if we name the variadic parameters. The values passed to a variadic parameter are made available within the closure’s body as an array of the appropriate type. Swift Closures allow only a single variadic parameter ‘…’

Syntax

{ (variadicParameterName: Type…) -> ReturnType in
}

Example 1

Following is a closure with a variadic parameter named “numbers” and a type of “Double…” and it is made available within the closure’s body as a constant array called numbers of type [Double]

let mean = { (numbers: Double…) -> Double in
     var total: Double = 0
     for number in numbers {
        total += number
     }
    return total / Double(numbers.count)
}
mean(1.2, 2.3)
// Output - 1.75

Example 2

Following is a closure with a variadic parameter named “names” and a type of “String…”

let websiteNames = { (names: String…) in
    print(names)
}
websiteNames("Apple", "Medium", "Google")
// Output - ["Apple", "Medium", "Google"]