Book Image

Hands-On Design Patterns with Kotlin

By : Alexey Soshin
Book Image

Hands-On Design Patterns with Kotlin

By: Alexey Soshin

Overview of this book

Design patterns enable you as a developer to speed up the development process by providing you with proven development paradigms. Reusing design patterns helps prevent complex issues that can cause major problems, improves your code base, promotes code reuse, and makes an architecture more robust. The mission of this book is to ease the adoption of design patterns in Kotlin and provide good practices for programmers. The book begins by showing you the practical aspects of smarter coding in Kotlin, explaining the basic Kotlin syntax and the impact of design patterns. From there, the book provides an in-depth explanation of the classical design patterns of creational, structural, and behavioral families, before heading into functional programming. It then takes you through reactive and concurrent patterns, teaching you about using streams, threads, and coroutines to write better code along the way By the end of the book, you will be able to efficiently address common problems faced while developing applications and be comfortable working on scalable and maintainable projects of any size.
Table of Contents (13 chapters)

Streams are lazy, collections are not

Be careful with those functions on large collections, though. Most of them will copy the collection for the sake of immutability.

Functions starting with as won't do that, though:

// Returns a view, no copy here
(1..10).toList().asReversed()

// Same here
(1..10).toList().asSequence()

To understand the difference, check the following code:

val numbers = (1..1_000_000).toList()
println
(measureTimeMillis {
numbers.stream().map {
it * it
}
}) // ~2ms

println(measureTimeMillis {
numbers.map {
it * it
}
}) // ~19ms

You'll notice that code using stream() actually never executes. Streams, being lazy, wait for a terminating function call. Functions on collections, on the other hand, execute one after the other.

If we add the terminating call though, we'll see totally different numbers:

println(measureTimeMillis {
...