Preface 2
1 val ints = if (checkCondition()) {
2 generateList()
3 } else {
4 emptyList()
5 }
As an additional bonus, another Kotlin feature called type inference liberates us from declaring ints
as List<Integer>.
Similarly, try/catch blocks in Java don’t return any values, so you have to declare necessary
variables before these blocks. Add the requirement to always catch or throw checked exceptions,
and you’ll get a recipe for crafting complex and difficult to maintain code. As you will see later in
this book, with Kotlin you don’t actually need to use try/catch blocks at all! Instead, it’s usually
better to wrap dangerous logic and return an Either object:
1 val resultT = eitherTry {
2 // invoke some dangerous code
3 }
This is only a fraction of features which enable Kotlin developers to write concise and easily readable
code. Of course, we will be discussing these features in detail throughout the book.
Since Kotlin tries to fit into the existing Java ecosystem, I decided to take Vert.x - a primarily Java
framework - and use it for developing our sample Web application. Basing our narrative on Vert.x
1
allows us to experience first-hand what it is like to use existing libraries in Kotlin.
Vert.x, however, is quite an unusual beast and differs from traditional frameworks in multiple ways.
First, it’s completely asynchronous and in this respect similar to NodeJS. Instead of blocking the
computation until the result becomes available, Vert.x uses callbacks:
1 router.get("/").handler { routingContext ->
2 routingContext.response().end("Hello World")
3 }
As a modern programming language, Kotlin comes with a first-class support for lambdas (function
literals) and therefore, allows to work with Vert.x in a pleasant, almost DSL-like way.
Second, Vert.x is not based on Servlets, which makes it a good choice for people without Java
background, especially Web developers. The fact that Vert.x comes with an embedded Web server
enables simple deployment and easy integration with frontend tools.
Writing a Web application usually involves using many additional tools. While Vert.x provides a lot
out of the box, it doesn’t provide everything we need. As a result, throughout the book, we will be
1
http://vertx.io/
