Book Image

Programming Kotlin

Book Image

Programming Kotlin

Overview of this book

Quickly learn the fundamentals of the Kotlin language and see it in action on the web. Easy to follow and covering the full set of programming features, this book will get you fluent in Kotlin for Android.

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Table of Contents (20 chapters)
Programming Kotlin
Programming Kotlin
Credits
Credits
About the Authors
About the Authors
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Customer Feedback
Customer Feedback
Preface
Preface
Free Chapter
1
Getting Started with Kotlin
Getting Started with Kotlin
Using the command line to compile and run Kotlin code
Kotlin runtime
The REPL
Kotlin for scripting
Kotlin with Gradle
Kotlin with Maven
IntelliJ and Kotlin
Eclipse and Kotlin
Mixing Kotlin and Java in a project
Summary
2
Kotlin Basics
Kotlin Basics
Vals and vars
Type inference
Basic types
Comments
Packages
Imports
String templates
Ranges
Loops
Exception handling
Instantiating classes
Referential equality and structural equality
This expression
Visibility modifiers
Control flow as expressions
Null syntax
When expression
Type hierarchy
Summary
3
Object-Oriented Programming in Kotlin
Object-Oriented Programming in Kotlin
Classes
Interfaces
Inheritance
Visibility modifiers
Abstract classes
Interface or abstract class
Polymorphism
Overriding rules
Inheritance versus composition
Class delegation
Sealed classes
Summary
4
Functions in Kotlin
Functions in Kotlin
Defining functions
Single expression functions
Member functions
Local functions
Top-level functions
Named parameters
Default parameters
Extension functions
Operators
Function literals
Tail recursive functions
Varargs
Standard library functions
Generic functions
Pure functions
Java from Kotlin
Kotlin from Java
Summary
5
Higher Order Functions and Functional Programming
Higher Order Functions and Functional Programming
Higher order functions
Closures
Anonymous functions
Function references
Function-literal receivers
Functions in the JVM
Function composition
Inline functions
Currying and partial application
Memoization
Type alias
Either
Custom DSLs
Validation and error accumulation
Summary
6
Properties
Properties
Why use properties?
Syntax and variations
Visibility
Late initialization
Delegated properties
Lazy initializations
Lateinit versus lazy
Observables
A non-null property delegate
Properties or methods?
Summary
7
Null Safety, Reflection, and Annotations
Null Safety, Reflection, and Annotations
Nullable types
Smart cast
Safe null access
Elvis operator
Safe casting
Optionals
Reflection
Constructors
Objects and companions
Useful KClass properties
Reflective functions and properties
Annotations
Standard annotations
Runtime annotation discovery
Summary
8
Generics
Generics
Parameterised functions
Parameterized types
Bounded polymorphism
Type variance
Nothing type
Type projection
Type erasure
Type reification
Recursive type bounds
Algebraic data types
Summary
9
Data Classes
Data Classes
Automatic creation of getters and setters
The copy method
toString out of the box
hashCode and equals methods generated for you
Destructed declarations
Destructing types
Data class definition rules
Limitations
Summary
10
Collections
Collections
Class hierarchy
Arrays
Lists
Maps
Sets
Read-only views
Indexed access
Sequences
Summary
11
Testing in Kotlin
Testing in Kotlin
Getting started
Choosing a spec
Matchers
Inspectors
Interceptors
Project config
Property testing
Table-driven testing
Tags, conditions, and config
Summary
12
Microservices with Kotlin
Microservices with Kotlin
Definition
Drawbacks
Why microservices?
Lagom
Defining services
Implementing a Lagom service
Summary
13
Concurrency
Concurrency
Threads
Deadlocks and livelocks
Executors
Race conditions
Summary

Type erasure

Kotlin is designed primarily as a language for the Java Virtual Machine (JVM), and when the JVM was first designed, generics were not included as a feature. Over time it became apparent that this was a major flaw of the language, and so in Java 1.5 (or Java SDK 5), released in 2004, generics were added as a feature to the compiler.

However, because of a desire to stay backwards compatible with previous versions of Java, the designers of Java decided that generics would be implemented using a technique called erasure. Erasure is the name given to the process by which the compiler removes type parameters during compilation.

In Java, a class defined as List<T> in the source code would be compiled simply as List, or List<Object>, if you like. This poses problems, some of which have already been introduced:

  • Functions with the same names and same erased parameters will clash. The fun print(list: List<String>) and fun print(list: List<Int) will have the same function...

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