Hands-On Design Patterns with Kotlin

Validation

How many times did you have to write code like this:

fun setCapacity(cap: Int) {    if (cap < 0) {        throw IllegalArgumentException()    }    ...}

Instead, you can check arguments with require():

fun setCapacity(cap: Int) {    require(cap > 0)}

This makes the code a lot more fluent.

You can use require() to check for nested nulls:

fun printNameLength(p: Profile) {    require(p.firstName != null)}

But there's also requireNotNull() for that:

fun printNameLength(p: Profile) {    requireNotNull(p.firstName)}

Use check() to validate the state of your object. This is useful when you provide some object that the user may not have set up correctly:

private class HttpClient {    var body: String? = null    var url: String = ""    fun postRequest() {        check(body !=  ...