Scala将函数作为参数传递给另一个函数

抱歉弄得一团糟。我在斯卡拉还是有办法的。将所有问题重新表述如下：

def func1(x: Double, y: Double) = {
  x+y
}

def func2(x: Double, y: Double) = {
  x-y
}

def calc(f: (Double, Double) => Double, z: Int) = {
  f(1,2) + z
}

//Sometimes I want to call
calc(func1(1,2), 3)

//Other times
calc(func2(1,2), 3)

我得到了这个错误：

<console>:52: error: type mismatch;
 found   : Double
 required: (Double, Double) => Double
              calc(func1(1,2), 3)
                        ^

什么是调用calc的正确方法

---

谢谢

首先，你正在使用一个变量。不想详细阅读更多信息，这被认为是一个不好的做法，如果你的映射打算在类中本地使用，你可以创建一个可变映射

回到你的问题： 如果希望函数按预期工作，那么应该确保doSomeComputing函数返回otherFunction所期望的值作为输入参数，如下所示

def doSomeComputation(m1: Map[String, List[(String, Double)]], name: String) = {
      (Map("some_key" -> List(("tuple1",1.0))), "tuple2")
}

返回类型为Map[String，List[String，Int]]，String

---

然而，这对你想做什么没有多大意义，如果你能清楚地提到你想实现什么，我可以帮助你理解。

注意，f的参数，即1和2，在calc的主体中提供

因此，您不需要为传入的函数指定任何参数

calc(func1, 3)
calc(func2, 3)

---

您需要传递函数签名f:Map[String，List[String，Double]]，String=>Double，而不仅仅是返回类型。下面是一个简单的例子：

var testMap: Map[String, List[(String, Double)]] = Map(
  "First" -> List(("a", 1.0), ("b", 2.0)),
  "Second" -> List(("c", 3.0), ("d", 4.0))
)
// testMap: Map[String,List[(String, Double)]] = Map(First -> List((a,1.0), (b,2.0)), Second -> List((c,3.0), (d,4.0)))

def doSomeComputation(m1: Map[String, List[(String, Double)]], name: String): Double = {
  m1.getOrElse(name, List[(String, Double)]()).map( x => x._2 ).max
}
// doSomeComputation: (m1: Map[String,List[(String, Double)]], name: String)Double

def doSomeOtherComputation(m1: Map[String, List[(String, Double)]], name: String): Double = {
  m1.getOrElse(name, List[(String, Double)]()).map( x => x._2 ).min
}
// doSomeOtherComputation: (m1: Map[String,List[(String, Double)]], name: String)Double

def otherFunction(f: (Map[String, List[(String, Double)]], String) => Double, otherName: String) = {
  f(testMap, "First") * otherName.length
}
// otherFunction: (f: (Map[String,List[(String, Double)]], String) => Double, otherName: String)Double

println(otherFunction(doSomeComputation, "computeOne"))
// 20.0

println(otherFunction(doSomeOtherComputation, "computeOne"))
// 10.0

---

根据您的用例，最好将testMap和name作为参数传递给其他函数。

这不是将函数作为参数传递，而是传递函数的结果。是的，您是对的

var testMap: Map[String, List[(String, Double)]] = Map(
  "First" -> List(("a", 1.0), ("b", 2.0)),
  "Second" -> List(("c", 3.0), ("d", 4.0))
)
// testMap: Map[String,List[(String, Double)]] = Map(First -> List((a,1.0), (b,2.0)), Second -> List((c,3.0), (d,4.0)))

def doSomeComputation(m1: Map[String, List[(String, Double)]], name: String): Double = {
  m1.getOrElse(name, List[(String, Double)]()).map( x => x._2 ).max
}
// doSomeComputation: (m1: Map[String,List[(String, Double)]], name: String)Double

def doSomeOtherComputation(m1: Map[String, List[(String, Double)]], name: String): Double = {
  m1.getOrElse(name, List[(String, Double)]()).map( x => x._2 ).min
}
// doSomeOtherComputation: (m1: Map[String,List[(String, Double)]], name: String)Double

def otherFunction(f: (Map[String, List[(String, Double)]], String) => Double, otherName: String) = {
  f(testMap, "First") * otherName.length
}
// otherFunction: (f: (Map[String,List[(String, Double)]], String) => Double, otherName: String)Double

println(otherFunction(doSomeComputation, "computeOne"))
// 20.0

println(otherFunction(doSomeOtherComputation, "computeOne"))
// 10.0