Steps

1. How to define an Option in a function parameter

Let's redo the example from the previous tutorial on Learn How To Create Function Parameters where we had provided a default value to the couponCode parameter.

To recap, our use case is that not all our customers who are buying donuts from our store would have a coupon code. Hence, the coupon code parameter should be optional.

In Scala, this means that you can declare couponCode using the Option type. Since our coupon code will be a String, couponCode parameter should be declared as: couponCode: Option[String]

println("Step 1: How to define an Option in a function parameter")
def calculateDonutCost(donutName: String, quantity: Int, couponCode: Option[String]): Double = {
  println(s"Calculating cost for $donutName, quantity = $quantity")

  couponCode match {
    case Some(coupon) =>
    val discount = 0.1 // Let's simulate a 10% discount
    val totalCost = 2.50 * quantity * (1 - discount)
    totalCost

    case None => 2.50 * quantity
  }
}

NOTE:

• Inside our function, we will test for a valid couponCode using pattern matching.
• In the case of Some(coupon), we assume a database lookup for the discount that needs to be applied. But, in our example, we will assume the discount is 10%.
• As part of the pattern matching, we also provide the None case where no couponCode was passed-through.

2. How to call a function which has an Option parameter

Let's use the function defined in Step 1 to calculate the cost for a customer buying 5 Glazed Donuts:

println("\nStep 2: How to call a function which has an Option parameter")
println(s"""Total cost = ${calculateDonutCost("Glazed Donut", 5, None)}""")

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

Step 2: How to call a function which has an Option parameter
Calculating cost for Glazed Donut, quantity = 5
Total cost = 12.5

NOTE:

• Since our customer does not have a couponCode, we had to supply a None as the couponCode parameter.
• Providing a None for every Option parameter is perhaps not very elegant. Fortunately, this is easily solved - see Step 3 below.

3. How to assign a default value to an Option parameter

To assign a default value of None as part of the declaration for couponCode parameter, you can use the following syntax:

println("\nStep 3: How to assign a default value to an Option parameter")
def calculateDonutCostWithDefaultOptionValue(donutName: String, quantity: Int, couponCode: Option[String] = None): Double = {
  println(s"Calculating cost for $donutName, quantity = $quantity")

  couponCode match{
    case Some(coupon) =>
      val discount = 0.1 // Let's simulate a 10% discount
      val totalCost = 2.50 * quantity * (1 - discount)
      totalCost

    case _ => 2.50 * quantity
  }
}

4. How to call a function whose Option parameter has a default value

Using the function defined in Step 3, you no longer have to pass-through a None value for the Option couponCode parameter.

If you have a legitimate couponCode to pass-through, you can use Some() as shown below:

println(\n"Step 4: How to call a function which has an Option parameter with a default value")
println(s"""Total cost = ${calculateDonutCostWithDefaultOptionValue("Glazed Donut", 5)}""")
println(s"""Total cost with discount = ${calculateDonutCostWithDefaultOptionValue("Glazed Donut", 5, Some("COUPON_1234"))}""")

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

Step 4: How to call a function which has an Option parameter with a default value
Calculating cost for Glazed Donut, quantity = 5
Total cost = 12.5
Calculating cost for Glazed Donut, quantity = 5
Total cost with discount = 11.25