Hands-On Serverless Applications with Kotlin by Hardik Trivedi

Author:Hardik Trivedi [Hardik Trivedi]
Language: eng
Format: epub
Publisher: Packt Publishing
Published: 2018-09-28T16:30:38+00:00

Lambda functions

One of the top-selling points of Kotlin is that it supports a function as a type. This means functions can be saved/held as an object or can be passed as a parameter, just like an object. You can think of lambda functions as functions without a name. We used to call them anonymous functions. Kotlin's lambda functions are similar to Java's lambda functions.

They are very useful. They save us a lot of time by not writing specific functions in an abstract class or an interface.

For example, a button's onClick event is one of the boring and stereotype works in Android. But Kotlin does it using lambdas:

createPollButton.setOnClickListener {

presenter.createPoll(pollTitle.text.toString(), pollQuestion.text.toString(), getSharedPreferences(getString(R.string.app_name), Context.MODE_PRIVATE).getString("userId", ""))

}

Let's say you want to write a function that adds two numbers but in a lambda style. The code can be written as follows:

val sum = { num1: Int, num2: Int -> num1 + num2 }

And we can call the preceding function using the following code:

val sumAns=sum(10,20)

The val sum just looks like a property, but it's actually a function. Many developers also use invoke functions, which trigger the lambda function. Using invoke, the same code can be rewritten like:

val sumAns=sum.invoke(10,20)

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