learning scala Function Composition andThen

 

• Ordering using andThen: f(x) andThen g(x) = g(f(x))
• Ordering using compose: f(x) compose g(x) = f(g(x))

 

 println("Step 1: Assume a pre-calculated total cost amount")
  val totalCost: Double = 10



  println("\nStep 2: How to define a val function to apply discount to total cost")
  val applyDiscountValFunction = (amount: Double) => {
    println("Apply discount function")
    val discount = 2 // fetch discount from database
    amount - discount
  }



  println("\nStep 3: How to call a val function")
  println(s"Total cost of 5 donuts with discount = ${applyDiscountValFunction(totalCost)}")



  println("\nStep 4: How to define a val function to apply tax to total cost")
  val applyTaxValFunction = (amount: Double) => {
    println("Apply tax function")
    val tax = 1 // fetch tax from database
    amount + tax
  }



  println("\nStep 5: How to call andThen on a val function")
  println(s"Total cost of 5 donuts = ${ (applyDiscountValFunction andThen applyTaxValFunction)(totalCost) }")

result:

Step 1: Assume a pre-calculated total cost amount

Step 2: How to define a val function to apply discount to total cost

Step 3: How to call a val function
Apply discount function
Total cost of 5 donuts with discount = 8

Step 4: How to define a val function to apply tax to total cost

Step 5: How to call andThen on a val function
Apply discount function
Apply tax function
Total cost of 5 donuts = 9