扩展函数的Scala缺少参数类型匿名函数的参数类型必须是完全已知的.(第8.5条)

Question

我有下面的片段需要完成一个赋值。为了实现这一要求，我必须正确地替换注释/*fulfill ...*/。然而，我尽了最大的努力，我仍然得到了

扩展函数缺少参数类型匿名函数的参数类型必须是完全已知的。(SLS 8.5(错误。

我发现了与此错误相关的类似问题。然而，我无法从这些答案中找到解决我的特殊问题的办法。

因此，目标是检查事件是否满足属性。

我很高兴得到每一个提示。

这是我需要完成的代码：

import scala.collection.mutable.MutableList
abstract class Event
case class Command(cmdName: String) extends Event
case class Succeed(cmdName: String) extends Event
case class Fail(cmdName: String) extends Event
class Property(val name: String, val func: () => Boolean)
class Monitor[T] {
val properties = MutableList.empty[Property]
// (propName: String)(formula: => Boolean) was inserted by me
def property(propName: String)(formula: => Boolean) /* fulfill declaration here */ {
properties += new Property(propName, formula _)
}
var eventsToBeProcessed = List[T]()
def check(events: List[T]) {
for (prop <- properties) {
eventsToBeProcessed = events
println(prop.func())                
}
}
def require(func: PartialFunction[T, Boolean]):Boolean = {
/* Fulfill body */
// This is what I came up with and what throws the compilation error
// case event:T => if (func.isDefinedAt(event)) Some(func(event)) else None
// Edit 1: Now I tried this but it prints that properties evaluate to false
var result = true
for (event <- eventsToBeProcessed){
if (func.isDefinedAt(event)){
result = result && func(event)
}
}
return  result
}
}
class EventMonitor extends Monitor[Event] {
property("The first command should succeed or fail before it is received again") {
require {
case Command(c) =>
require {
case Succeed(`c`) => true
case Fail(`c`) => true
case Command(`c`) => false
}
}
}
property("The first command should not get two results") {
require {
case Succeed(c) =>
require {
case Succeed(`c`) => false
case Fail(`c`) => false
case Command(`c`) => true
}
case Fail(c) =>
require {
case Succeed(`c`) => false
case Fail(`c`) => false
case Command(`c`) => true
}
}
}
property("The first command should succeed") {
/* Add a property definition here which requires that the first command does not fail.
* It should yield OK with the events listed in the main method.
*/
// This is what I came up with
require{
case Command(c) =>
require{
case Succeed(`c`)=> true
case Fail(`c`) => false
}
}
}
}
object Checker {
def main(args: Array[String]) {
val events = List(
Command("take_picture"),
Command("get_position"),
Succeed("take_picture"),
Fail("take_picture")
)
val monitor = new EventMonitor
monitor.check(events)
// Desired output should be "true false true"
}
}

Answer 1

您编写了require函数，该函数返回Boolean的T => Option[Boolean]整数。你应该把它重写成这样的东西：

def require(func: PartialFunction[T, Boolean]):Boolean = {
val left = eventsToBeProcessed.dropWhile(!func.isDefinedAt(_))
left.headOption.forall(head => {
eventsToBeProcessed = left.tail
func(head)
})
}