2
考慮下面的代碼規則:什麼是Scala的解決衝突的隱含價值
/**
* Created by danap on 12/8/15.
*/
object ImplicitTest {
trait EC {
override def toString : String = s"EC"
}
trait DEC extends EC {
def sub : EC
override def toString : String = s"DEC - $sub"
}
def usesEC(implicit ec : EC) = ec.toString
class B(implicit val dec: DEC) {
def whichEC = usesEC
}
class C(implicit val dec: DEC) {
implicit val _ec = dec.sub
def whichEC = usesEC
def whichECExplicit = usesEC(_ec)
}
def main(args:Array[String]): Unit = {
implicit val dec : DEC = new DEC {
val sub = new EC {}
}
val b = new B
val c = new C
println(s"b class = ${b.whichEC}")
println(s"c class = ${c.whichEC}")
println(s"c class = ${c.whichECExplicit}")
}
}
斯卡拉2.11的輸出是:
b class = DEC - EC
c class = DEC - EC
c class = EC
我希望它是:
b class = DEC - EC
c class = EC
c class = EC
因爲隱含的val _ec
被聲明爲「更接近」調用usesEC
whichEC
。爲什麼會發生?另外,我可能會如何強制_ec
在C.whichEC
中隱式使用?
在scala中使用implicits時的個人規則#1:從來沒有超過一個相同類型的範圍,因爲你永遠不知道是誰在壓倒誰。 –