Delegated Properties Example in Kotlin

DelegatedPropertiesExample.kt

import ExampleDelegates.accumulator
import ExampleDelegates.uppercase
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

fun main() {
    val person = Person("ala1222", 12)

    println(person.name)//ALA1222
    println(person.balance) //12
    person.balance = 30
    println(person.balance)//42
}

class Person {
    var name: String by uppercase()
    var balance: Int by accumulator()

    constructor(name: String, balance: Int) {
        this.name = name
        this.balance = balance
    }
}

object ExampleDelegates {

    public fun uppercase(): ReadWriteProperty<Any?, String> = UpperCase()
    public fun accumulator(): ReadWriteProperty<Any?, Int> = Accumulator()

    private class UpperCase : ReadWriteProperty<Any?, String> {
        private var value: String? = null

        public override operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
            return value ?: throw IllegalStateException(
                "Property ${property.name} should be initialized before get."
            )
        }

        public override operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
            this.value = value.toUpperCase()
        }
    }

    private class Accumulator : ReadWriteProperty<Any?, Int> {
        private var value: Int = 0

        public override operator fun getValue(thisRef: Any?, property: KProperty<*>): Int {
            return value
        }

        public override operator fun setValue(thisRef: Any?, property: KProperty<*>, value: Int) {
            this.value = this.value.plus(value)
        }
    }
}