What are high-level functions in Kotlin?

High-order functions are functions that take other functions as parameters or return a function as a result.

Examples of usage:

• Passing functions as arguments: Allows creating more flexible and reusable code.

  fun operate(x: Int, y: Int, operation: (Int, Int) -> Int): Int {
      return operation(x, y)
  }
  
  fun main() {
      val sum = operate(5, 3) { a, b -> a + b } // Lambda as an argument
      println(sum) // 8
  }
  

• Returning functions from other functions: Allows creating functions that generate other functions.

  fun mathOperation(op: String): (Int, Int) -> Int {
      return when (op) {
          "sum" -> { a, b -> a + b }
          "subtract" -> { a, b -> b - a }
          else -> throw IllegalArgumentException("Unknown operation")
      }
  }
  
  fun main() {
      val add = mathOperation("sum")
      println(add(10, 5)) // 15
  }
  

Advantages:

• Improved readability: Lambdas and function references make the code more concise and understandable.
• More flexibility: Allow abstraction from specific execution logic.
• Simplification of API: Often used in Kotlin's standard libraries (e.g., in collection functions).

Examples of standard high-order functions:

• forEach
• map
• filter
• reduce
• apply
• let
• run
• with

High-order functions together with lambda expressions are a key feature of functional programming in Kotlin.