在Scala中，我如何以无状态，功能性的方式建立银行账户？

Question

根据OO范例，您可能会有类似

的内容

class BankAccount(balance: Double) {
    def deposit(...)
    def withdraw(...)

}

我想知道你如何在功能范例中做同等的事情？

Answer 1

让BankAccount类中的每个方法都返回一个具有新余额的新BankAccount对象。这样，余额可以是不可变的变量。

class BankAccount(balance: Double) {
    def deposit(amount: Double): BankAccount
    def withdraw(amount: Double): BankAccount
}

Answer 2

将帐户设为一系列交易，而不仅仅是当前金额：

case class Transaction(numberOfSeashells: Int)
case class Account(transactions: Iterable[Transaction])

def addNewTransaction(startingBalance: Int, t: Transaction) = startingBalance + t.numberOfSeashells
def balance(account: Account) = account.transactions.foldLeft(0)(addNewTransaction)

val acct = Account(List(Transaction(3), Transaction(-1)))
val newBalance = balance(acct)

结果：

scala>   val acct = Account(List(Transaction(3), Transaction(-1)))
acct: Account = Account(List(Transaction(3), Transaction(-1)))

scala>   val newBalance = balance(acct)
newBalance: Int = 2

这样你就可以删除无效的交易（退款等）。