How to use Variadic Parameters in Swift 5+?

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A variadic parameter accepts zero or more values of a specified type. When creating API it seems more developer-friendly as we don’t needs to generate an array at the caller site in order to pass multiple arguments.

The variadic parameter using three dots can be passed a varying number of input values when the function is called.

KEY TAKEWAYS

The values passed to a variadic parameter are made available within the function’s body as an array of the appropriate type.

// Variadic parameter can be used any number of arguments(here voucherValues)
func redeemVouchers(_ greetings: String, voucherValues: Int...) -> String {
    let voucherText = voucherValues.count > 0 ? " You have redeemed " + "\(voucherValues.reduce(0, +)) €" : ""
    return greetings + voucherText
}

// No variadic parameter
redeemVouchers("Congratulation!")
// "Congratulation!"

// Multiple variadic parameter
redeemVouchers("Congratulation!", voucherValues: 12, 23, 10)
// "Congratulation! You have redeemed 45 €"

// Single variadic parameter
redeemVouchers("Congratulation!", voucherValues: 10)
// "Congratulation! You have redeemed 10 €"

Recently released Swift 5.4 brings support for multiple variadic parameters. However, you can not use variadic parameters as inout parameters.

func redeemVouchers(_ greetings: String..., voucherValues: String...) {
  ...
}

redeemVouchers("Congratulation!" "Mr. Robot", voucherValues: 12, 23, 10)

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