以下函数在我看来是尾递归的
但是如果我在它上面加@tailrec
,编译器仍会抱怨:
def loop(newInterests: Set[Interest], oldInterests: Set[Interest]): Set[Interest] = {
newInterests.headOption.fold(oldInterests){ ni =>
val withSameKeyWord = oldInterests.find(oi => oi.keyword == ni.keyword)
withSameKeyWord.fold(loop(newInterests.tail, oldInterests + ni)){ k =>
loop(newInterests.tail,
oldInterests - k + k.copy(count = k.count + 1))
}
}
}
答案 0 :(得分:7)
如thefourtheye所述,您的函数返回fold
s的结果。尾递归版(带模式匹配)看起来像:
@tailrec
def loop(newInterests: Set[Interest], oldInterests: Set[Interest]): Set[Interest] = {
newInterests.headOption match {
case None => oldInterests
case Some(ni) =>
oldInterests.find(oi => oi.keyword == ni.keyword) match {
case None => loop(newInterests.tail, oldInterests + ni)
case Some(k) => loop(newInterests.tail, oldInterests - k + k.copy(count = k.count + 1))
}
}
}