Kotlin Functional Programming Tutorial: Lambda Expressions, Higher-Order Functions, Inline Functions, and Anonymous Functions

This Kotlin Functional Programming tutorial explains key functional programming concepts including lambda expressions, higher-order functions, inline functions, and anonymous functions. Each topic is explained with practical examples and best practices to help developers write clean, concise, and reusable Kotlin code using functional paradigms.

Kotlin Functional Programming – Complete Tutorial

Lambda Expressions

Lambda expressions are anonymous functions that can be treated as values. They are widely used in functional programming and collection operations.

Syntax


val sum: (Int, Int) -> Int = { a, b -> a + b }

Example


fun main() {
val multiply: (Int, Int) -> Int = { a, b -> a * b }
println(multiply(5, 3)) // 15

val numbers = listOf(1, 2, 3, 4, 5)
val squared = numbers.map { it * it }
println(squared) // [1, 4, 9, 16, 25]
}

Best Practices

  1. Use lambdas for concise, inline functions.
  2. Prefer descriptive parameter names when complex logic is used.

Higher-Order Functions

Higher-order functions are functions that take other functions as parameters or return functions.

Example


fun calculate(a: Int, b: Int, operation: (Int, Int) -> Int): Int {
return operation(a, b)
}

fun main() {
val sum = calculate(10, 5) { x, y -> x + y }
val multiply = calculate(10, 5) { x, y -> x * y }
println(sum) // 15
println(multiply) // 50
}

Best Practices

  1. Use higher-order functions to make code flexible and reusable.
  2. Keep functions small and focused for clarity.

Inline Functions

Inline functions improve performance by reducing the overhead of function calls when higher-order functions are used.

Example


inline fun operate(a: Int, b: Int, action: (Int, Int) -> Int): Int {
return action(a, b)
}

fun main() {
val result = operate(6, 3) { x, y -> x - y }
println(result) // 3
}

Best Practices

  1. Use inline for small functions passed as parameters.
  2. Avoid inlining very large functions, as it increases code size.

Anonymous Functions

Anonymous functions are like lambdas but with explicit fun keyword and optional return type.

Syntax


val greet = fun(name: String): String {
return "Hello, $name"
}

Example


fun main() {
val greet = fun(name: String): String {
return "Hello, $name"
}
println(greet("Muni")) // Hello, Muni
}

Best Practices

  1. Use anonymous functions when lambda syntax is insufficient or readability requires explicit return.
  2. Prefer lambdas for simplicity when possible.

Summary

This chapter introduced Kotlin functional programming concepts including lambda expressions, higher-order functions, inline functions, and anonymous functions. Applying these concepts helps write concise, reusable, and expressive code, especially when working with collections and event-driven programming.