Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

data class Address(
    val street: String,
    val city: String,
    val zip: String,
)

data class User(
    val id: Int,
    val name: String,
    val email: String,
    val address: Address,
)

fun main() {
    val addr  = Address("123 Main St", "Springfield", "12345")
    val user1 = User(1, "Alice", "alice@example.com", addr)

// toString — auto-generated, deeply nested
    println(user1)

// Structural equality
    val user2 = User(1, "Alice", "alice@example.com", addr)
    println(user1 == user2)    // true
    println(user1 === user2)   // false — different objects

// copy — change only specific fields
    val updatedUser = user1.copy(
        email   = "alice@newdomain.com",
        address = addr.copy(city = "Shelbyville"),
    )
    println(updatedUser)

// Destructuring
    val (id, name, email) = user1
    println("id=$id  name=$name  email=$email")

// Works as map key (hashCode consistent with equals)
    val userMap = mapOf(user1 to "active", updatedUser to "pending")
    println(userMap[user2])   // active (user2 == user1)
}