Number helpers

Add number conversion and calculation functions.

Int extension

This lesson adds the squared extension to Int. It returns the square of the number.

Example: fun Int.squared(): Int { return this * this }. Here this is the receiver value, the Int the function was called on. Calling 5.squared() returns 25. Extension functions give a natural syntax as if the methods belonged to the receiver type; this is why they are preferred for helper functions in Kotlin.

Chained calls

Extension functions can be chained like normal methods. This makes data-processing pipelines readable.

Example: 5.squared() is a single call. But chaining like "hello world".titleCase().length is possible. The type returned by one extension can host another extension call. In this lesson 5.squared() returns 25; this result is an Int and can be the receiver of further Int extensions.

Exercise Add the Int.squared extension

Alongside the existing Helpers object and String.titleCase extension, add an Int.squared() extension function. Its body returns this * this. In main print Helpers.greet("Alex"), "hello world".titleCase() and 5.squared() with println.

Show example solution

object Helpers {
    fun greet(name: String): String {
        return "Hello, $name!"
    }
}

fun String.titleCase(): String {
    return split(" ").joinToString(" ") { word ->
        word.lowercase().replaceFirstChar { it.uppercase() }
    }
}

fun Int.squared(): Int {
    return this * this
}

fun main() {
    println(Helpers.greet("Alex"))
    println("hello world".titleCase())
    println(5.squared())
}

Test yourself

In <code>fun Int.squared(): Int { return this * this }</code>, what does <code>this</code> refer to?
- The Helpers object
- The Int value it was called on
- A class instance
- The main function
Show answer

The Int value it was called on — In an extension this is the value of the receiver type.

Complete the Int extension definition

fun ____.squared(): Int {
    return this * this
}

Show answer

fun Int.squared(): Int {
    return this * this
}

Match the Int extension parts

fun Int.squared()

Receiver and method
this * this

Square computation
5.squared()

Call
return 25

Result

Next lesson: Date helpers

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