Data Class trong Kotlin

data class User(
    val name: String,
    val age: Int,
    val email: String
)
 
fun main() {
    val user = User("Alice", 25, "alice@email.com")
    println(user)  // User(name=Alice, age=25, email=alice@email.com)
}

data class Person(val name: String, val age: Int)
 
fun main() {
    val p1 = Person("Alice", 25)
    val p2 = Person("Alice", 25)
    
    // equals()
    println(p1 == p2)  // true
    
    // hashCode()
    println(p1.hashCode() == p2.hashCode())  // true
    
    // toString()
    println(p1)  // Person(name=Alice, age=25)
}

data class User(val name: String, val age: Int)
 
fun main() {
    val user1 = User("Alice", 25)
    
    // Copy với thay đổi
    val user2 = user1.copy(age = 26)
    println(user2)  // User(name=Alice, age=26)
    
    // Copy nguyên bản
    val user3 = user1.copy()
}

data class Point(val x: Int, val y: Int)
 
fun main() {
    val point = Point(10, 20)
    
    // Destructuring
    val (x, y) = point
    println("x=$x, y=$y")  // x=10, y=20
    
    // Trong lambda
    val points = listOf(Point(1, 2), Point(3, 4))
    points.forEach { (x, y) -> println("$x, $y") }
}

data class Config(
    val host: String = "localhost",
    val port: Int = 8080,
    val secure: Boolean = false
)
 
fun main() {
    val default = Config()
    val custom = Config(port = 3000, secure = true)
    
    println(default)  // Config(host=localhost, port=8080, secure=false)
    println(custom)   // Config(host=localhost, port=3000, secure=true)
}

data class Person(val name: String) {
    // Không tham gia equals, hashCode, toString
    var age: Int = 0
}
 
fun main() {
    val p1 = Person("Alice")
    val p2 = Person("Alice")
    
    p1.age = 25
    p2.age = 30
    
    println(p1 == p2)  // true (chỉ so sánh name)
}

data class Address(val city: String, val street: String)
 
data class Person(
    val name: String,
    val address: Address
)
 
fun main() {
    val person = Person(
        "Alice",
        Address("Hanoi", "123 Main St")
    )
    println(person)
}

// Regular class - phải tự implement
class RegularUser(val name: String, val age: Int) {
    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is RegularUser) return false
        return name == other.name && age == other.age
    }
    
    override fun hashCode() = 31 * name.hashCode() + age
    override fun toString() = "RegularUser(name=$name, age=$age)"
}
 
// Data class - tự động có sẵn
data class DataUser(val name: String, val age: Int)

// ✅ Correct
data class Valid(val x: Int)  // Ít nhất 1 property
 
// ❌ Không được abstract, open, sealed, inner
// abstract data class Wrong(val x: Int)
// open data class Wrong(val x: Int)
 
// ✅ Có thể implement interface
interface Printable { fun print() }
data class Doc(val content: String) : Printable {
    override fun print() = println(content)
}