我有一个我知道是尾递归的函数。但是由于我定义它的方式,编译器抱怨该函数在非尾部位置具有递归调用。这就是功能。
@tailrec
def travel: (Int, List[Char]) => Int = {
case (n, Nil) => n
case (n, '~' :: sls) => travel(0, sls)
case (n, '^' :: sls) => travel(max(n-1,0), sls)
case (n, '>' :: sls) => travel(n+1, sls)
case (_, s :: sls) => throw new IllegalArgumentException("Illegal selector '" + s + "'")
}
我明白了
error: could not optimize @tailrec annotated method travel: it contains a recursive call not in tail position
def travel: (Int, List[Char]) => Int = {
如果我这样写,它工作正常。
@tailrec
def travel(n:Int, l:List[Char]): Int = (n,l) match {
case (n, Nil) => n
case (n, '~' :: sls) => travel(0, sls)
case (n, '^' :: sls) => travel(max(n-1,0), sls)
case (n, '>' :: sls) => travel(n+1, sls)
case (_, s :: sls) => throw new IllegalArgumentException("Illegal selector '" + s + "'")
}
我认为这与def: (Input) => Output = {}
类型声明风格有关。我使用它是因为它看起来比编写嵌套匹配或元组匹配更简洁。