Lambda functions are anonymous functions that can be assigned to a variable and passed around like any other value. Lambdas are super useful and convenient as they allow you to write a less code, while also improving the readability of your codebase by removing extra boilerplate.

val add: (Int, Int) -> Int = { x, y -> x + y }

val addition = { x, y : -> x + y }

The two lambdas above take in two Int parameters and return an Int. The second lambda takes advantage of type inference, and can be even shorter.

If a lambda only takes in 1 parameter, you can shorten it further by using the reserved it keyword:

val double = { 2 * it }

val square = { it * it }

Using lambdas allow us to simplify more complex functions. Wihout lambda:

interface Callback {
  fun onCallback(result: String)
}

fun doAsync(x : Int, callback: Callback) {
  callback.onCallback("done")
}

doAsync(20, object : Callback {
  override fun onCallback(result: String) {
    print(result)
  }
}

With lambda:

fun doAsync (x : Int, callback: (String) -> Unit) {
  callback("done")
}

doAsync(20) { result -> print(result)}

Iterating over collections also becomes really easy with the help of lambdas:

var allItems = listOf(1.99, 2.50, 7.49, 9.99, 25.0)

val priceyItems = prices.filter { it > 5.0 }

Lambdas can help in making your codebase more reusable, succint and easier to mantain.

To learn more about Lambdas see Higher-Order Functions and Lambdas - Kotlin Programming Language