我在package
对象中有这个方法:
def extractLoop[@specialized T](x: Map[T, T]) = {
val whatever = x.head
val stop = whatever._1
def iteration(
acc: Seq[T] = Seq(whatever._1, whatever._2),
last: T = whatever._2): Seq[T] = {
val next = x(last)
if (next == stop) acc
else iteration(acc :+ next, next)
}
iteration()
}
但我还不明白,为什么编译器(我有2.9.2版本)说type T is unused or used in non-specializable positions.
?
答案 0 :(得分:5)
我认为原因很简单,你使用的是Map[T, T]
并非专业。
一些例子:
scala> class MyMap[A,B]
defined class MyMap
scala> def extractLoop[@specialized T](x: MyMap[T, T]) = {
| sys.error("TODO")
| }
<console>:8: warning: type T is unused or used in non-specializable positions.
def extractLoop[@specialized T](x: MyMap[T, T]) = {
^
extractLoop: [T](x: MyMap[T,T])Nothing
但是如果你将MyMap
专门用于它的两个类型参数,则没有警告:
scala> class MyMap[@specialized A,@specialized B]
defined class MyMap
scala> def extractLoop[@specialized T](x: MyMap[T, T]) = {
| sys.error("TODO")
| }
extractLoop: [T](x: MyMap[T,T])Nothing