Scala 错误：找到列表 [Char]，需要列表 [ScalaObject]

发布于 2024-10-04 05:10:03 字数 714 浏览 3 评论 0原文

我有这段 Scala 代码片段：

def prologList(l: List[ScalaObject], sep: String) =
    "[" + (if (l isEmpty) "" else l.reduceLeft(_ + sep + _)) + "]"

def neighbors(s: State) = prologList(trans(s).toList, ", ")
def labels(s: State) = prologList(labeling(s).toList, ", ")

倒数第二行编译正常，但在最后一行出现错误

找到List[Char]，需要List[ScalaObject]

（labeling 的类型为 Map[State, Set[Char]]< /code>。）

我有点惊讶，因为 1）我认为 List[Char] 可以被视为 List[ScalaObject] 的子类型（而不是到 Java），2）最后一行上面的行编译！（虽然 trans 的类型为 Map[State, Set[State]]...）

问题很明显，我做错了什么，以及如何修复它？

原文

I have this snippet of Scala code:

def prologList(l: List[ScalaObject], sep: String) =
    "[" + (if (l isEmpty) "" else l.reduceLeft(_ + sep + _)) + "]"

def neighbors(s: State) = prologList(trans(s).toList, ", ")
def labels(s: State) = prologList(labeling(s).toList, ", ")

The next-to-last line compiles fine, but on the last line I get the error

Found List[Char], required List[ScalaObject]

(labeling has the type Map[State, Set[Char]].)

I'm a bit surprised, since 1) I thought that List[Char] could be seen as a subtype of List[ScalaObject] (as opposed to Java), and 2) the line above the last line compiles! (trans has type Map[State, Set[State]] though...)

The question is obvious, what am I doing wrong, and how do I fix it?

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

司马昭之心 2024-10-11 05:10:03

Char 不是 ScalaObject 的子类型。

顶部有 Any，它是所有内容的超类型。您可能可以将 ScalaObject 替换为 Any ，这样您的代码就可以编译。

请参阅 http://www.scala-lang.org/node/128 了解类型层次结构图。

在 REPL 中，您可以使用隐式函数来解决类型关系问题：

scala> implicitly[Char <:< Any]
res0: <:<[Char,Any] = <function1>

scala> implicitly[Char <:< ScalaObject]
<console>:6: error: could not find implicit value for parameter e: <:<[Char,ScalaObject]
       implicitly[Char <:< ScalaObject]
                 ^

scala> implicitly[List[Char] <:< List[Any]]
res2: <:<[List[Char],List[Any]] = <function1>

scala> implicitly[List[Char] <:< List[ScalaObject]]
<console>:6: error: could not find implicit value for parameter e: <:<[List[Char],List[ScalaObject]]
       implicitly[List[Char] <:< List[ScalaObject]]

编辑：顺便说一句，您知道 mkString 吗？

trans(s).mkString("[", ", ", "]")

Char is not a subtype of ScalaObject.

At the top you have Any which a super type of everything. You can probably replace ScalaObject with Any and that should make your code compile.

See http://www.scala-lang.org/node/128 for a type hierarchy diagram.

In the REPL you can use the implicitly function to troubleshoot type relationships:

scala> implicitly[Char <:< Any]
res0: <:<[Char,Any] = <function1>

scala> implicitly[Char <:< ScalaObject]
<console>:6: error: could not find implicit value for parameter e: <:<[Char,ScalaObject]
       implicitly[Char <:< ScalaObject]
                 ^

scala> implicitly[List[Char] <:< List[Any]]
res2: <:<[List[Char],List[Any]] = <function1>

scala> implicitly[List[Char] <:< List[ScalaObject]]
<console>:6: error: could not find implicit value for parameter e: <:<[List[Char],List[ScalaObject]]
       implicitly[List[Char] <:< List[ScalaObject]]

Edit: by the way, do you know about mkString?