我想要这样的东西:
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
}
我不是在寻找基于通用 HashMap 的记忆化像这样 https://stackoverflow.com/questions/25129721/how-does-this-scala-memo-works。我尝试使用它来实现它var Option[A]
但它对我来说看起来不太惯用:
private var cachedResponse: Option[A] = None
def get: A = cachedResponse getOrElse {
cachedResponse = Option(db.findModel())
cachedResponse.get
}
def update: Unit = {
db.updateModel
cachedResponse = None
}
标准库中没有内置的。
Using a var
包含不可变的Option
是惯用的方法(假设你不能重写它以完全不使用状态)。
否则,您应该构建自己的。这是实现的核心:
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:paste
如果使用 REPL。
本文内容由网友自发贡献,版权归原作者所有,本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容,请联系:hwhale#tublm.com(使用前将#替换为@)