Kotlin Lambda Expression

What is not a Lambda?

If you wonder how to distinguish between a lambda and a regular function, you are on the right track.

fun main() {
   val student = Student("Coding Ninjas",10)
   student.printNameWithMarks()
}

 
class Student(private val name: String, private val score: Int) {
   fun printNameWithMarks() {
       println(name + score)
   }
}

Output:

Coding Ninjas10

The above example is one such example here. We can see that lambdas are not class or function bodies. They are simply a part of basic syntax declaration.

fun main() {
  val number = 10
  val no = if(number % 2 == 0) {
      "$number is Even"
  } else {
      "$number is Odd"
  }
  println(no)
}

Output:

10 is Even

Here, it might look like lambda, but it isn't. Also, the if-else block doesn't represent a function, so we can say that this is not a lambda expression.

Return Type of Lambda Expression

Here is a modified version of the above example, but we are using lambda here.

fun main() {
  val no = fun(number: Int): String {
      return if (number % 2 == 0) {
          "$number is Even"
      } else {
          "$number is Odd"
      }
  }
  println(no(1001))
}

Here we have made no variable that takes a function with number as a parameter. Then we will return the String according to the condition.

Note: If you want to learn more about If Else, head over to this article.

Type Expression in Lambda

Let us now understand different types of Lambdas expressions. First, look at the example below.

fun main() {
  val noArguments = { println("0") }
  val oneArgument = { a: String -> println(a) }
  val twoArguments = { a: Int, b: String -> println("$a + $b") }
  val multipleArguments = { a: String ->
      if (a.isEmpty()) {
          println("$a is empty")
      } else {
          println("$a is not empty")
      }
  }
  noArguments.invoke()
  oneArgument("one")
  twoArguments(2, "two")
  multipleArguments("codingNinjas")
}

Here we have defined different argument types. Note that we have used invoke() to run a lambda expression that has no arguments.

We can give any number of arguments in lambda expression or define any multiple statement lambda expression.

Output:

0
one
2 + two
codingNinjas is not empty

Complex Lambda Expression

Lambdas Expression can be easy to read when it has one or two arguments, but It can go complex once using it with other functions.

fun main() {
  println(listOf(1, 2, 3, 4).fold(1) { n1, n2 -> n1 * n2 })
}

Here, we are using the fold function, which will start from index 0, and the default value of fold would be one as we have supplied in fold(1). Here, we have applied lambda expression with two arguments: the current item and the contemporary accumulated item. This code will multiply all of the items in the list and get 24 as output.

The above output is one of the examples of trailing lambdas. If the lambda is the only argument in the call, we can omit the parentheses entirely.

fun main() {
  run { println("Only Argument") }
}

FAQs

1. Why is there a need for Lambda Expression?
   A lambda expression is a reduced form of a function. It can be supplied as a parameter, saved as a variable, or returned as a value. It is widely used in those interfaces where there is only one abstract method.
    
2. Can we pass Lambda as a Function Expression?
   In Kotlin, we can pass Lambda Expression in the function argument. We can also give Lambda Expression in a nested lambda expression.
    
3. Can we call Lambda Expression an Anonymous Function?
   Yes, lambda expressions and anonymous functions are both function literals. We can call lambda expressions anonymous functions.

Key Takeaways

Cheers if you reached here!! 

The purpose of this article was to introduce you to the Kotlin Lambda Expression, the basic syntax of using this expression and understand the need for Lambda Expression in Android Development.

If you want to learn more about Kotlin Higher-Order and Inline Function in Kotlin, then you can jump to this article which covers them in great detail.

However, learning never stops, and there is more to learn. So head over to our Android Development Course on the Coding Ninjas Website to dive deep into Android Development and build future applications. Till then, Happy Learning!