Summary - Functional programming
- Kotlin course
- Advanced
- Lesson 54/83
- 5 min
Combine immutability, Sequence and Result to write a functional pipeline.
Summary - Functional programming
In this group you saw the core of functional programming: immutability with data class, pure functions, laziness with Sequence, accumulation with fold and the monad approach with Result.
This lesson includes a small task that combines three of them: you will define a data class and compute a total with fold. This pattern is the foundation of functional Kotlin.
Practice Summary: Product and fold
Define a data class Product(val name: String, val price: Int). In main create a list of three products, compute the total price with fold(0) { acc, p -> acc + p.price } and print it with println.
Starter code
// Product data class: name and price properties
// in main list three products, compute total with foldSample solution
data class Product(val name: String, val price: Int)
fun main() {
val items = listOf(
Product("Bread", 20),
Product("Milk", 15),
Product("Tea", 25)
)
val total = items.fold(0) { acc, p -> acc + p.price }
println(total)
}Expected output
60
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which is a core feature of functional programming?
- Immutable data Correct answer
- Lots of side effects
- Frequent global state mutation
- Loops everywhere
Explanation: Immutability is core to functional programming.
2 Match the FP concepts
| Term | Meaning |
|---|---|
data class |
Immutability |
fun double(n) |
Pure function |
asSequence() |
Laziness |
fold(0) |
Accumulation |
3 Complete the fold call
val total = items.____(0) { acc, item -> acc + item.price }val total = items.fold(0) { acc, item -> acc + item.price }Explanation: fold accumulates with an initial value.