So far we have not talked about the interoperability with Java. We have to do before returning an object (and simply return null if it is null) then The most common reason to use apply is the initialisation of an object. For example letʼs suppose we have a class Greeter which has a function hello thatīy default prints a greeting message on the standard output:Ĭlass Greeter In Kotlin when you declare a variable, a field or a function parameter, by default they cannotīe null. This problem is to use some kind of Option monad.Īs weʼll soon see Kotlin actually does not introduce any new special wrapper type - it uses regular Java It is quite interesting - especially at times like these when the most popular way of handling One of the first features a Kotlin developer learns is the languageʼs approach to handling null values. Shiny server-side system using Kotlin as its primary language and we do not regret it. Therefore at Allegro we decided to give it a chance - we built our new Its history however dates a few years backĪnd itʼs mature and stable enough to be used for developing solid reliable applications. To encourage people to sign up, during the registration process, the only information you ask for is an email address and a password.Kotlin may seem like a new kid on the block - itʼs been officially released only in February. For instance, imagine that you’re writing code for the next great social network app. Possibly the most tempting time to use a null value is when a field in a class or method won’t be initialized immediately. Initialize var fields with Option, not null If you’re working with a Java library that returns null, convert it to an Option, or something else.When a method doesn’t produce the intended result, you may be tempted to return null.When a var field in a class or method doesn’t have an initial default value, initialize it with Option instead of null.There are several common situations where you may be tempted to use null values, so this recipe demonstrates how not to use null values in those situations:
I just imagine that there is no such thing as a null, and write my code in other ways.
Period.”Īlthough I’ve used null values in this book to make some examples easier, in my own practice, I no longer use them.
Solutionĭavid Pollak, author of the book Beginning Scala, offers a wonderfully simple rule about null values: Tony Hoare, inventor of the null reference way back in 1965, refers to the creation of the null value as his “billion dollar mistake.” In keeping with modern best practices, you want to eliminate null values from your code. This is Recipe 20.5, “Scala best practice: Eliminate null values from your code.” Problem This is an excerpt from the 1st Edition of the Scala Cookbook (partially modified for the internet). show more info on classes/objects in repl.
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