斯卡拉 – 任何人都能给我一个很好的例子吗？这种关于“什么使一

class Account {
  private var balance = 0
  def getBalance = balance
  def deposit(amount: Int): Unit = balance += amount
}

class NoVarAccount {
  val account = new Account()
  def balance = account.getBalance
  def deposit(amount: Int) = account.deposit(amount)
}

现在,NoVarAccount没有任何var,但它仍然是有状态的,因为它转发了对Account的调用,这确实是有状态的.

实际上,您无法保证在同一对象上调用两次平衡将获得相同的结果.

val account = new NoVarAccount()
account.balance // 0
account.deposit(42)
account.balance // 42

在此示例中,account.balance不是引用透明的,即您不能将account.balance替换为其返回值,因为它可能会有所不同.

相反,无国籍帐户将如下：

class StatelessAccount(val balance: Int = 0) {
  def deposit(amount: Int) = new StatelessAccount(balance + amount)
}

甚至更具风俗性：

case class StatelessAccount(balance: Int = 0) {
  def deposit(amount: Int) = this.copy(balance = balance + amount))
}

在这种情况下,余额是参考透明的：

val account = StatelessAccount()
account.balance // 0
val account2 = account.deposit(42)
account2.balance // 42
account.balance // still 0