User.kt

class User {
    var name: String = ""
    var email: String = ""
    var age: Int = 0
    var address: String = ""

    override fun toString(): String {
        return "User(name='$name', email='$email', age=$age, address='$address')"
    }
}

class UserBuilder {
    private var user = User()

    fun name(name: String): UserBuilder {
        user.name = name
        return this
    }

    fun email(email: String): UserBuilder {
        user.email = email
        return this
    }

    fun age(age: Int): UserBuilder {
        user.age = age
        return this
    }

    fun address(address: String): UserBuilder {
        user.address = address
        return this
    }

    fun build(): User {
        return user
    }
}

val user = UserBuilder()
    .name("John Smith")
    .email("john.smith@example.com")
    .age(30)
    .address("123 Main St")
    .build()

println(user)
// Output: User(name='John Smith', email='john.smith@example.com', age=30, address='123 Main St')