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

State

You can think of the State design pattern as an opinionated Strategy pattern, which we discussed at the beginning of this chapter. But while the Strategy pattern is usually replaced from the outside by the client, the state may change internally based solely on the input it gets.

Look at this dialog a client wrote with the Strategy pattern:

  • Client: Here's a new thing to do, start doing it from now on.
  • Strategy: OK, no problem.
  • Client: What I like about you is that you never argue with me.

Compare it with this one:

  • Client: Here's some new input I got from you.
  • State: Oh, I don't know. Maybe I'll start doing something differently. Maybe not.

The client should also expect that the state may even reject some of its inputs:

  • Client: Here's something for you to ponder, State.
  • State: I don't know what it is! Don't you see I'm busy? Go bother some Strategy with this!

So, why do clients...