class Person {
    var name: String = ""
    val age: Int = 0
}

var name: String = ""
    get() = field.toUpperCase()
    set(value) {
        field = "Name: $value"
    }

class Person {
    var name: String = ""
        get() = field.toUpperCase()  // возвращает значение поля name в верхнем регистре
        set(value) {
            field = value.trim()    // устанавливает значение поля name без начальных и конечных пробелов
        }
}

class Example {
    var p: String by Delegate()
}

class Person(val name: String, var age: Int) {
    var id: Int = 0

    // require выдает ошибку с указанным текстом, если условие в левой части false
    init {
        require(name.isNotBlank(), { "У человека должно быть имя!" })
        require(age > -1, { "Возраст не может быть отрицательным." })
    }

    constructor(name: String, age: Int, id: Int) : this(name, age) {
        if (id > 0) this.id = id * 2
    }
}

    init {
        ...
    }

    // и т.д.
}

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

val person = Person("Alice", 29)
val (name, age) = person

println(name) // Alice
println(age) // 29

val people = listOf(Person("Alice", 30), Person("Bob", 40))
for ((name, age) in people) {
    println("$name is $age years old")
}

// Alice is 30 years old
// Bob is 40 years old

class Person(val firstName: String, val lastName: String, val age: Int) {
    operator fun component1() = firstName
    operator fun component2() = lastName
    operator fun component3() = age
}

val person = Person("John", "Doe", 30)
val (firstName, lastName, age) = person
println("$firstName $lastName is $age years old.")

open class Fraction {
  ...
}

open class Fraction {

  open fun toAttack() {
    ...
  }

}

open class Fraction {

  open val name: String = "default"

  open fun toAttack() {
    ...
  }

}

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

fun main() {
    val person = Person("John", 30)
    println(person::class) // выводит "class Person"
}

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

fun main() {
    val person = Person("John", 30)
    println(person.javaClass) // выводит "class Person"
}

sealed class Shape {
    class Circle(val radius: Double) : Shape()
    class Rectangle(val width: Double, val height: Double) : Shape()
    class Triangle(val base: Double, val height: Double) : Shape()
}

fun calculateArea(shape: Shape): Double {
    return when (shape) {
        is Shape.Circle -> Math.PI * shape.radius * shape.radius
        is Shape.Rectangle -> shape.width * shape.height
        is Shape.Triangle -> 0.5 * shape.base * shape.height
    }
}

fun main() {
    val circle = Shape.Circle(5.0)
    val rectangle = Shape.Rectangle(2.0, 3.0)
    val triangle = Shape.Triangle(4.0, 5.0)

    println(calculateArea(circle))     // Output: 78.53981633974483
    println(calculateArea(rectangle))  // Output: 6.0
    println(calculateArea(triangle))   // Output: 10.0
}