How to Use Variadic Parameters in Swift?

A function is a block of code that is used to perform some specified task. It is reusable and saves time and resources from writing the same code again and again. The syntax of the Swift function is flexible enough to create simple as well as complex functions. A function definition contains its name, parameters list, and return value. It is not necessary for a function to always contain a parameter list or return type, it depends upon the need of the user. In Swift language, a function supports three types of parameters: default parameters, in-out parameters, and variadic parameters. By default, a function contains constant parameters which are also known as default parameters, here the constant parameter means the value of the function cannot be changed and if we try to change then the compiler will give an error. The general syntax for creating a function is:

Syntax:

func functionName(parameterName: type) -> returnType{

// Body of the function

}

Now we will discuss variadic parameters.

Variadic Parameters

In Swift, variadic parameters are the special type of parameters available in the function. It is used to accept zero or more values of the same type in the function. It is also used when the input value of the parameter is varied at the time when the function is called. In the Swift function, when we are working with variadic parameters then it is necessary that the values passed to the variadic parameter must be used inside the function’s body as an array of a specific type. A single function can contain multiple variadic parameters and it is necessary that the parameter comes after the first variadic parameter that contains the argument label. It will make parameters unambiguous so that it is easy for the compiler to understand which argument is passed to which parameters(that is variadic and the parameter comes after the variadic parameter). In a function, a variadic parameter is created using three-period characters(…).

Syntax:

func functionName(_parameterName: type …) -> returnType{

// Function body

}

Example:

Swift

// Swift program to illustrate variadic parameter
import Swift

// Creating a function with variadic parameter
// Here this function find the total marks of semester 1
func StudentResult(_ marks:Int...) -> Int{
    var sum = 0

    // Finding the sum of the given marks
    for i in marks{
        sum += i
    }
    return sum
}

// Calling function with a list of parameters
// Marks of all the subjects
var summ = StudentResult(23, 45, 66, 77, 88, 66)

// Displaying the result
print("Total marks of semester 1: ", summ)

Output:

Total marks of semester 1:  365

Variadic parameters with other parameters

In function, we can are allowed to use variadic parameters along with other parameters. When we are using a variadic parameter with other parameters then the variadic parameter is placed at the first position then the other parameters are used. It is necessary for the parameter that comes after the first variadic parameter must contain the argument label because it will make parameters unambiguous so that it is easy for the compiler to understand which argument is passed to which parameter either for variadic or the parameter that comes after the variadic parameter.

Syntax:

func functionName(_parameterName: type …, parameterName2: type, parameterName3: type) -> returnType{

// Function body

}

Example:

Swift

// Swift program to illustrate variadic parameter with other parameters
import Swift

// Creating a function with variadic and default parameter
// Here this function find the total marks of semester 1
// and name of the student
func StudentResult(_ marks:Int..., Sname: String){

    var sum = 0

    // Finding the sum of the given marks
    for i in marks{
        sum += i
    }

    // Displaying the name of the student and result
    print("Name of the student: ", Sname)
    print("Total marks of semester 1: ", sum)
}

// Calling function with a list of parameters
// that is variadic and default parameter
// Marks of all the subjects and name of the student
StudentResult(23, 45, 66, 77, 88, 66, Sname: "Rohan")

Output:

Name of the student:  Rohan
Total marks of semester 1:  365

Multiple Variadic parameters

A swift function can contain multiple variadic parameters starting from Swift 5.4. The earlier version of Swift doesn’t support multiple variadic parameters in the function, if you try to use them you will get a compiler error. In multiple variadic parameters, it is necessary that all the variadic parameters must contain the argument label because it will make parameters unambiguous so that it is easy for the compiler to understand which argument is passed to which parameters. If we do not use the argument label at the time of calling the function then the compiler assigned all the values to the first parameter and the remaining parameters remains unassigned.

Syntax:

func functionName(_parameterName1: type …, parameterName2: type…, parameterName3: type…) -> returnType{

// Function body

}

Example:

Swift

// Swift program to illustrate multiple variadic parameters
import Swift

// Creating a function with multiple variadic parameters
// Here this function find the total marks of semester 1, 2, 3, and 4
func StudentResult(_ sem1:Int..., sem2: Int..., sem3: Int..., sem4: Int... ){

    var sum1 = 0
    var sum2 = 0
    var sum3 = 0
    var sum4 = 0

    // Finding the sum of the given marks of semester 1
    for i in sem1{
        sum1 += i
    }
    // Finding the sum of the given marks of semester 2
    for j in sem2{
        sum2 += j
    }
    // Finding the sum of the given marks of semester 3
    for k in sem3{
        sum3 += k
    }
    // Finding the sum of the given marks of semester 4
    for l in sem4{
        sum4 += l
    }

    // Displaying the result
    print("Total marks of semester 1: ", sum1)
    print("Total marks of semester 2: ", sum2)
    print("Total marks of semester 3: ", sum3)
    print("Total marks of semester 4: ", sum4)
}

// Calling function with multiple variadic parameters
// Marks of all four semesters
StudentResult(30, 45, 66, 77, 88, 66,
              sem2: 45, 67, 34, 67, 89,54,
              sem3: 98, 87, 86, 76, 78, 71,
              sem4: 90, 80, 76, 71, 61, 52)

Output:

Total marks of semester 1:  372
Total marks of semester 2:  356
Total marks of semester 3:  496
Total marks of semester 4:  430