Scala类型不匹配;找到:需要布尔值:List [Int]

Question

我试图用简单的例子来解决我的sbt测试

package example
object Lists {
    def sum(xs: List[Int]): Int = {

        xs match {
      case x :: tail => x + sum(tail)
      case Nil => 0
     }
    }
    def max(xs: List[Int]): Int = {
      xs match {
        case Nil => throw new java.util.NoSuchElementException()
        case List(x) => x
        case x :: y :: rest => max ((if (x > y) x else y) :: rest)  
    }
    }

  }

第二个文件可以从http://www.filedropper.com/listssuite_1下载

当我尝试用sbt测试时

[error] /home/milenko/dom1/example/src/test/scala/example/ListsSuite.scala:122: type mismatch;
[error]  found   : Boolean
[error]  required: List[Int]
[error]     assert(sum(List() === 0))
[error]                       ^
[error] /home/milenko/dom1/example/src/test/scala/example/ListsSuite.scala:134: type mismatch;
[error]  found   : Boolean
[error]  required: List[Int]
[error]       assert(max(List(1, -4, 2, 6) === 6))
[error]                                    ^
[error] two errors found
[error] (test:compileIncremental) Compilation failed
[error] Total time: 1 s, completed 17/03/2017 10:43:00

我不明白为什么会这样.如果编译器发现我的类型为布尔值？

Answer 1

这是错误的:

assert(sum(List() === 0))

因为sum参数的类型是boolean(List() === 0)

尝试: assert(sum(List()) === 0)改为.

最大功能也是如此.