Scala中抽象类方法内安全实现对象状态变更：克隆与不可变模式

abstract class A {
  var dbName: String // 使用var定义可变属性

  def withConfig(db: String): A = {
    var a = this // 'a' 引用了当前的this实例
    a.dbName = db // 直接修改了原对象的dbName
    a
  }
}

class A1(db: String) extends A {
  override var dbName: String = db
}

object TestInitial {
  def main(args: Array[String]): Unit = {
    var obj = new A1("TEST")
    println(s"Original dbName before modification: ${obj.dbName}") // Output: TEST
    var newObj = obj.withConfig("TEST2")
    println(s"New object dbName: ${newObj.dbName}") // Output: TEST2
    println(s"Original dbName after modification: ${obj.dbName}") // Output: TEST2 (原对象被修改)
  }
}

abstract class A {
  var dbName: String

  def withConfig(db: String): A = {
    var a = this.clone().asInstanceOf[A] // 尝试克隆，但会抛出异常
    a.dbName = db
    a
  }
}
// ... (A1, A2 class definitions remain the same)

// 运行将抛出:
// Exception in thread "main" java.lang.CloneNotSupportedException: c.i.d.c.A1

abstract class A extends Cloneable { // 抽象类A需要继承Cloneable接口
  var dbName: String

  def withConfig(db: String): A = {
    // 调用clone()方法，并强制转换为A类型
    var a = this.clone().asInstanceOf[A]
    a.dbName = db // 修改新对象的dbName
    a
  }
}

class A1(db: String) extends A {
  override var dbName: String = db
  // 在具体子类中重写clone()方法，返回一个该类的新实例
  override def clone(): AnyRef = new A1(db)
}

class A2(db: String) extends A {
  override var dbName: String = db
  override def clone(): AnyRef = new A2(db)
}

object TestCloneable {
  def main(args: Array[String]): Unit = {
    var obj = new A1("TEST")
    println(s"Original dbName: ${obj.dbName}") // Output: Original dbName: TEST
    var newObj = obj.withConfig("TEST2")
    println(s"New object dbName: ${newObj.dbName}") // Output: New object dbName: TEST2
    println(s"Original dbName after withConfig: ${obj.dbName}") // Output: Original dbName after withConfig: TEST
  }
}

abstract class A {
  def db: String // 使用val或def定义不可变属性
  def withConfig(db: String): A // 返回一个新A实例
}

class A1(val db: String) extends A { // db作为val参数，使其不可变
  override def withConfig(db: String): A = new A1(db) // 返回一个A1的新实例
}

class A2(val db: String) extends A {
  override def withConfig(db: String): A = new A2(db) // 返回一个A2的新实例
}

object TestImmutable {
  def main(args: Array[String]): Unit = {
    val obj = new A1("TEST")
    println(s"Original db: ${obj.db}") // Output: Original db: TEST
    val newObj = obj.withConfig("TEST2")
    println(s"New object db: ${newObj.db}") // Output: New object db: TEST2
    println(s"Original db after withConfig: ${obj.db}") // Output: Original db after withConfig: TEST
  }
}