Book Image

Kotlin Design Patterns and Best Practices - Second Edition

By : Alexey Soshin
Book Image

Kotlin Design Patterns and Best Practices - Second Edition

By: Alexey Soshin

Overview of this book

This book shows you how easy it can be to implement traditional design patterns in the modern multi-paradigm Kotlin programming language, and takes you through the new patterns and paradigms that have emerged. This second edition is updated to cover the changes introduced from Kotlin 1.2 up to 1.5 and focuses more on the idiomatic usage of coroutines, which have become a stable language feature. You'll begin by learning about the practical aspects of smarter coding in Kotlin, as well as understanding basic Kotlin syntax and the impact of design patterns on your code. The book also provides an in-depth explanation of the classical design patterns, such as Creational, Structural, and Behavioral families, before moving on to functional programming. You'll go through reactive and concurrent patterns, and finally, get to grips with coroutines and structured concurrency to write performant, extensible, and maintainable code. By the end of this Kotlin book, you'll have explored the latest trends in architecture and design patterns for microservices. You’ll also understand the tradeoffs when choosing between different architectures and make informed decisions.
Table of Contents (17 chapters)
1
Section 1: Classical Patterns
6
Section 2: Reactive and Concurrent Patterns
11
Section 3: Practical Application of Design Patterns

Making asynchronicity explicit

As you saw in the previous chapter, it is very easy to create an asynchronous function in Kotlin. Here is an example:

fun CoroutineScope.getResult() = async { 
   delay(100) 
   "OK" 
}

However, this asynchronicity may be an unexpected behavior for the user of the function, as they may expect a simple value.

What do you think the following code prints?

println("${getResult()}")

For the user, the preceding code somewhat unexpectedly prints the following instead of "OK":

> Name: DeferredCoroutine{Active}@...

Of course, if you have read Chapter 6, Threads and Coroutines, you will know that what's missing here is the await() function:

println("${getResult().await()}")

But it would have been a lot more obvious if we'd named our function accordingly, by adding an async suffix:

fun CoroutineScope.getResultAsync() = async { 
   delay...