Scala:函数组合中的类型不匹配，发现 (Int, Int) => Seq[Int] require ？ => 序列[整数]

Question

我试图在一个脚本中组合 2 个函数，但遇到了无法解决的类型不匹配问题。 这是示例代码:

def generate(start: Int, end: Int): Seq[Int] = (start until end).toSeq
def restrain(seq: Seq[Int]) = seq.dropWhile(_ < 20).takeWhile(_ < 60)

val com: (Int, Int) => Seq[Int] = (restrain _ compose generate)

通过将其加载到 REPL 中:

:load test.sc

我收到以下错误:

       val com: (Int, Int) => Seq[Int] = (restrain _ compose generate)
                                                             ^
test.sc:1: error: type mismatch;
        found   : (Int, Int) => Seq[Int]
        required: ? => Seq[Int]

我做错了什么？

Answer 1

类型 Function2[Int, Int, Seq[Int]] 和 Function1[(Int, Int), Seq[Int]] 不同。 (generate _) 生成前者，而对于此组合，您需要后者。尝试:

restrain _ compose (generate _).tupled