Kotlin Reflection

Reflection Features

val kClass = String::class
println(kClass.simpleName) // "String"

val function = ::println
function("Hello!") // Calls println

val prop = Person::name
println(prop.get(person)) // Gets name

kClass.memberFunctions.forEach {
    println("Function: ${it.name}")
}

🔹 Class Reflection

Inspect class information at runtime:

import kotlin.reflect.full.*

data class Student(
    val id: Int,
    var name: String,
    var grade: Double
) {
    fun study() = println("$name is studying")
    fun getGradeLevel(): String = when {
        grade >= 90 -> "A"
        grade >= 80 -> "B"
        else -> "C"
    }
}

fun main() {
    val student = Student(1, "John", 85.5)
    val kClass = student::class
    
    // Class information
    println("Class: ${kClass.simpleName}")
    println("Is data class: ${kClass.isData}")
    
    // Properties
    println("\nProperties:")
    kClass.memberProperties.forEach { prop ->
        println("- ${prop.name}: ${prop.get(student)}")
    }
    
    // Functions
    println("\nFunctions:")
    kClass.memberFunctions.forEach { func ->
        println("- ${func.name}")
    }
}

🔹 Function References

Reference and call functions dynamically:

class Calculator {
    fun add(a: Int, b: Int): Int = a + b
    fun multiply(a: Int, b: Int): Int = a * b
    fun greet(name: String) = println("Hello, $name!")
}

fun topLevelFunction(message: String) {
    println("Top level: $message")
}

fun main() {
    val calc = Calculator()
    
    // Method references
    val addRef = Calculator::add
    val multiplyRef = calc::multiply  // Bound to instance
    
    println("Add: ${addRef(calc, 5, 3)}")      // Need instance
    println("Multiply: ${multiplyRef(4, 6)}")  // Already bound
    
    // Function reference as parameter
    val operations = listOf(Calculator::add, Calculator::multiply)
    operations.forEach { operation ->
        println("Result: ${operation(calc, 2, 3)}")
    }
    
    // Top-level function reference
    val topRef = ::topLevelFunction
    topRef("Reflection is cool!")
}

🔹 Property References

Access and modify properties dynamically:

import kotlin.reflect.full.*

class User(var name: String, var email: String, val id: Int) {
    var isActive: Boolean = true
}

fun main() {
    val user = User("Alice", "[email protected]", 123)
    val kClass = user::class
    
    // Get all mutable properties
    val mutableProps = kClass.memberProperties.filterIsInstance>()
    
    println("Original values:")
    mutableProps.forEach { prop ->
        println("${prop.name}: ${prop.get(user)}")
    }
    
    // Modify properties dynamically
    mutableProps.forEach { prop ->
        when (prop.name) {
            "name" -> (prop as kotlin.reflect.KMutableProperty1).set(user, "Bob")
            "email" -> (prop as kotlin.reflect.KMutableProperty1).set(user, "[email protected]")
            "isActive" -> (prop as kotlin.reflect.KMutableProperty1).set(user, false)
        }
    }
    
    println("\nModified values:")
    mutableProps.forEach { prop ->
        println("${prop.name}: ${prop.get(user)}")
    }
}

🔹 Practical Example: JSON Serializer

Use reflection to create a simple JSON serializer:

import kotlin.reflect.full.*

data class Product(val id: Int, val name: String, val price: Double, val inStock: Boolean)

fun Any.toJson(): String {
    val kClass = this::class
    val properties = kClass.memberProperties
    
    val jsonPairs = properties.map { prop ->
        val value = prop.get(this)
        val jsonValue = when (value) {
            is String -> "\"$value\""
            is Boolean, is Number -> value.toString()
            null -> "null"
            else -> "\"$value\""
        }
        "\"${prop.name}\": $jsonValue"
    }
    
    return "{${jsonPairs.joinToString(", ")}}"
}

fun main() {
    val product = Product(1, "Laptop", 999.99, true)
    val json = product.toJson()
    
    println("Product as JSON:")
    println(json)
    
    // Test with different object
    data class Person(val name: String, val age: Int, val city: String?)
    val person = Person("Alice", 30, null)
    
    println("\nPerson as JSON:")
    println(person.toJson())
}