أدوات Getter وSetter مخصصة مع field

class Circle(val radius: Double) {
    val area: Double
        get() = Math.PI * radius * radius
}
fun main() {
    val c = Circle(3.0)
    println(c.area) // ~28.27
}

class Rectangle(val w: Int, val h: Int) {
    val area get() = w * h
    val perimeter get() = 2 * (w + h)
}
fun main() {
    val r = Rectangle(3, 4)
    println("${r.area}, ${r.perimeter}") // 12, 14
}

class Temperature {
    var celsius: Double = 0.0
        set(value) {
            require(value >= -273.15) { "below absolute zero" }
            field = value
        }
}
fun main() {
    val t = Temperature()
    t.celsius = 25.0
    println(t.celsius)
    // t.celsius = -300.0 // throws
}

class Counter {
    var count: Int = 0
        set(value) {
            println("Setting count from $field to $value")
            field = value
        }
}
fun main() {
    val c = Counter()
    c.count = 5
    c.count = 10
}

class Brightness {
    var level: Int = 50
        set(value) {
            val clamped = value.coerceIn(0, 100)
            println("Brightness -> $clamped")
            field = clamped
        }
}
fun main() {
    val b = Brightness()
    b.level = 75
    b.level = 150 // clamps to 100
    println(b.level)
}

class Score {
    var value: Int = 0
        private set
    fun increment() { value++ }
    fun reset() { value = 0 }
}
fun main() {
    val s = Score()
    s.increment(); s.increment()
    println(s.value) // 2
    // s.value = 100 // ERROR: setter is private
}

class Email {
    var address: String = ""
        set(value) {
            require(value.contains("@")) { "invalid email" }
            field = value
        }
}
fun main() {
    val e = Email()
    e.address = "ada@example.com"
    println(e.address)
}

class Profile(_name: String?) {
    var rawName: String? = _name
    val displayName: String
        get() = rawName ?: "(unset)"
}
fun main() {
    val p = Profile(null)
    println(p.displayName) // (unset)
}

class Box {
    val readOnly: Int get() = 42
    var readWrite: Int = 0
}
fun main() {
    println(Box().readOnly)
    val b = Box(); b.readWrite = 5; println(b.readWrite)
}

class Wrong {
    var x: Int = 0
        set(value) {
            // x = value // INFINITE RECURSION — calls setter again
            field = value // CORRECT
        }
}
fun main() {
    val w = Wrong(); w.x = 42; println(w.x)
}