我想要这样的事情：
private val cachedResponse = mutable.Option.empty[A]
def get: A = cachedResponse getOrElseUpdate db.findModel()
def update: Unit = {
db.updateModel
cachedResponse.empty() // set it to None/Option.empty
}
我不是在寻找基于HashMap的通用memoization like this。我尝试使用var Option[A]来实现它，但它对我来说看起来不是很惯用：
private var cachedResponse: Option[A] = None
def get: A = cachedResponse getOrElse {
cachedResponse = Option(db.findModel())
cachedResponse.get
}
def update: Unit = {
db.updateModel
cachedResponse = None
}
答案 0 :(得分：5)
标准库中没有内置。
使用包含不可变var的{{1}}是惯用的方法（假设您无法重写此内容而根本不使用状态）。
否则，你应该建立自己的。这是实施的核心：
Option如果使用REPL，则与class MutableOpt[A] {
private[this] var myValue: A = _
private[this] var loaded = false
private def valueEquals(o: Any) = myValue == o
def get = if (loaded) myValue else throw new NoSuchElementException("MutableOpt")
def set(a: A): this.type = { loaded = true; myValue = a; this }
def getOrSet(a: => A): A = {
if (!loaded) {
myValue = a
loaded = true
}
myValue
}
def isEmpty = !loaded
def nonEmpty = loaded
def foreach[U](f: A => U): Unit = if (loaded) f(myValue)
def transform(f: A => A): this.type = { if (loaded) myValue = f(myValue); this }
def clear(): this.type = { loaded = false; this }
def toOption = if (loaded) Some(myValue) else None
override def toString = if (loaded) "MutableOpt("+myValue.toString+")" else "MutableOpt()"
override def hashCode = if (loaded) myValue.hashCode else 1751
override def equals(o: Any) = o match {
case m: MutableOpt[_] =>
(isEmpty && m.isEmpty) || (nonEmpty && m.nonEmpty && m.valueEquals(myValue))
case _ => false
}
}
object MutableOpt {
def from[A](o: Option[A]) = {
val m = new MutableOpt[A]
o match {
case Some(a) => m set a
case _ =>
}
m
}
}
一起定义。