Kotlin Functions


Mastering Metaprogramming: A Deep Dive into Kotlin Reflection

Kotlin, the statically typed programming language from JetBrains, offers an array of advanced features, and among the most powerful of these is Kotlin Reflection. With Kotlin Reflection, you can inspect and manipulate your code during runtime. This opens the door to metaprogramming: the act of writing code that can read, generate, analyze, or transform other code.

Mastering Metaprogramming: A Deep Dive into Kotlin Reflection

This article delves into Kotlin Reflection, showcasing its utility and providing hands-on examples to illustrate its metaprogramming capabilities.

1. Basics of Kotlin Reflection

Reflection in Kotlin is facilitated by the `kotlin-reflect` library. You’ll need to include this in your build file to access reflection features:

implementation "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"

Once set up, you can access the class metadata of any object using the `::class` syntax:

val stringType = "Hello, World!"::class
println(stringType)  // Prints: class kotlin.String

2. Inspecting Classes and Properties

With Kotlin Reflection, you can delve deep into classes, their properties, and functions.

Example: Fetching Class Properties

data class Person(val name: String, val age: Int)

val personClass = Person::class
for (property in personClass.memberProperties) {
// Outputs:
// name
// age

3. Invoking Functions Dynamically

Kotlin Reflection allows you to call functions in a dynamic fashion, offering flexibility during runtime.

fun greet(message: String) {
    println("Greeting: $message")

val greetFunction = ::greet
greetFunction.call("Hello Kotlin Reflection!")
// Outputs: Greeting: Hello Kotlin Reflection!

4. Accessing Annotations

Annotations are crucial for meta-information, and Kotlin Reflection seamlessly integrates with them.

annotation class Info(val description: String)

@Info(description = "Sample class for demonstration.")
class Sample

val annotations = Sample::class.annotations
for (annotation in annotations) {
    if (annotation is Info) {
// Outputs: Sample class for demonstration.

5. Modifying Mutable Properties

Reflection also enables property modification for mutable properties:

data class MutablePerson(var name: String, var age: Int)

val person = MutablePerson("Alice", 25)
val propName = MutablePerson::name

propName.setter.call(person, "Bob")

println(person.name)  // Outputs: Bob

6. Working with Constructor Parameters

Instantiating objects dynamically is a breeze with Kotlin Reflection:

data class Animal(val species: String, val habitat: String)

val constructor = Animal::class.primaryConstructor!!
val lion = constructor.call("Lion", "Savannah")

println(lion)  // Outputs: Animal(species=Lion, habitat=Savannah)

7. A Practical Use Case: Simple Object Mapper

Imagine you want to map data from one object to another without using third-party libraries. Kotlin Reflection is here to help!

data class Source(val name: String, val age: Int)
data class Destination(var name: String = "", var age: Int = 0)

fun mapData(source: Source, destination: Destination) {
    val sourceProperties = Source::class.memberProperties
    for (property in sourceProperties) {
        val value = property.get(source)
        val destProperty = Destination::class.memberProperties.find { it.name == property.name }
        destProperty?.let {
            (it as KMutableProperty<*>).setter.call(destination, value)
val source = Source("Emma", 30)
val destination = Destination()
mapData(source, destination)

println(destination)  // Outputs: Destination(name=Emma, age=30)


Kotlin Reflection is a potent tool for metaprogramming. It grants developers the ability to inspect and manipulate code dynamically during runtime, ushering in vast possibilities for code generation, analysis, and transformation.

From inspecting classes to working with annotations, functions, properties, and even creating simple object mappers, Kotlin Reflection has you covered. Dive deep into its extensive documentation, explore its vast capabilities, and leverage its power to craft advanced, dynamic, and flexible Kotlin applications.

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