Steps

1. How to define function which takes variable number of arguments

As a simple example, let's define a function named printReport() and it will have a single variable argument which represents the names of donuts for which we will print a report.

def printReport(names: String*) {
println(s"""Donut Report = ${names.mkString(" - ")}""")
}

NOTE:

• The names argument is of type String, but it is also a variable argument as we've defined it using the * syntax.
• As a variable argument, you will be allowed to call the printReport() function by passing zero or many parameters of type String as shown in Step 2 below.

2. How to call function which takes variable number of String arguments

Since the printReport() function takes a variable argument called names of type String, you are allowed to call the function with zero or many String values.

println("\nStep 2: How to call function which takes variable number of String arguments")
printReport("Glazed Donut", "Strawberry Donut", "Vanilla Donut")
printReport("Chocolate Donut")

You should see the following output when you run your Scala application in IntelliJ:

Step 2: How to call function which takes variable number of String arguments
Donut Report = Glazed Donut - Strawberry Donut - Vanilla Donut
Donut Report = Chocolate Donut

3. How to pass a List to a function with variable number of arguments

What if you had a variable argument function and had to pass in a List to it?

println("\nStep 3: How to pass a List to a function with variable number of arguments")
val listDonuts: List[String] = List("Glazed Donut", "Strawberry Donut", "Vanilla Donut")
printReport(listDonuts)

NOTE:

• Calling printReport() function by passing it the listDonuts value which is a List of type String will give you a compiler error!

Instead, you will need to use a special syntax called type ascription as follows:

printReport(listDonuts: _*)

You should see the following output when you run your Scala application in IntelliJ:

Step 3: How to pass a List to a function with variable number of arguments
Donut Report = Glazed Donut - Strawberry Donut - Vanilla Donut

4. How to pass a Sequence to a function with variable number of arguments

What if you had a variable argument function and had to pass in a Sequence to it?

println("\nStep 4: How to pass a Sequence to a function with variable number of arguments")
val seqDonuts: Seq[String] = Seq("Chocolate Donut", "Plain Donut")
printReport(listDonuts)

NOTE:

• Calling printReport() function by passing it the seqDonuts value which is a Sequence of type String will give you a compiler error!

Instead, you will need to use a special syntax called type ascription as follows:

printReport(seqDonuts: _*)

You should see the following output when you run your Scala application in IntelliJ:

Step 4: How to pass a Sequence to a function with variable number of arguments
Donut Report = Glazed Donut - Strawberry Donut - Vanilla Donut

5. How to pass an Array to a function with variable number of arguments

What if you had a variable argument function and had to pass in a Array to it?

println("\nStep 5: How to pass an Array to a function with variable number of arguments")
val arrDonuts: Array[String] = Array("Coconut Donut")
printReport(arrDonuts)

NOTE:

• Calling printReport() function by passing it the arrDonuts value which is a Array of type String will give you a compiler error!

Instead, you will need to use a special syntax called type ascription as follows:

printReport(arrDonuts: _*)

You should see the following output when you run your Scala application in IntelliJ:

Step 5: How to pass an Array to a function with variable number of arguments
Donut Report = Coconut Donut