我通常使用特征实施策略(一些行动,不需要附带的领域)。最近我发现可以用对象来定义相同的功能。它们可直接扩展功能性状或应用()什么是最好的策略在斯卡拉:对象或特质
示例代码扩展预留一些特质定义特殊的方法:
/* strategy realization via traits */
package object Traitness {
trait Strategy {
def performAction() : Unit =()
}
abstract class Usage {_ : Strategy =>
def doWork() =
this.performAction()
}
// defining strategies
trait SayA extends Strategy {
override def performAction() = {
println("A")
super.performAction()
}
}
trait SayB extends Strategy {
override def performAction() = {
println("B")
super.performAction()
}
}
trait SayC extends Strategy {
override def performAction() = {
println("C")
super.performAction()
}
}
//using strategies
class SimpleStrategy extends Usage with SayA
def reverseOrder() = new Usage with SayC with SayA
object fullUsage extends Usage with SayA with SayB with SayC
//run-time checking
val check1 : Boolean = (new SimpleStrategy).isInstanceOf[SayB]
val check2 : Boolean = reverseOrder().isInstanceOf[SayB]
val check3 : Boolean = fullUsage.isInstanceOf[SayB]
//compile-time checking
def proclaim(x : SayB) = println("SayB")
}
/* strategy realization via function objects */
package object Valueness {
trait Strategy extends Function0[Unit]
class Usage(val strategies : List[Strategy]) {
def doWork() = for (s <- strategies)
s()
}
//defining strategies
object SayA extends Strategy {
override def apply() = {
println("A")
}
}
object SayB extends Strategy {
override def apply() = {
println("B")
}
}
object SayC extends Strategy {
override def apply() = {
println("C")
}
}
//using strategies
class SimpleStrategy extends Usage(SayA :: Nil)
def reverseOrder() = new Usage(SayB :: SayA :: Nil)
val fullUsage = new Usage(SayA :: SayB :: SayC :: Nil)
//run-time checking
def check(strategy : Strategy, usage : Usage) = usage.strategies contains strategy
val check1 : Boolean = check(SayB, new SimpleStrategy)
val check2 : Boolean = check(SayB, reverseOrder())
val check3 : Boolean = check(SayB, fullUsage)
//no compile-time checking available
}
哪一个我应该选择?
这是非常相似的成分(proxy'ing来处理不同的策略对象)与继承(其中实现不同性状混合战略)..我认为这不是天生“最好”(或“更可取”),不同的情况可能适合不同的策略。 – 2012-12-01 18:37:55
使用自我类型不是强制性的。我可以混合使用策略,并将它们作为类型策略的类成员包含在用法中。 – ayvango