Question

这两个定义之间有什么区别？：

def sayTwords(word1: String, word2: String) = println(word1 + " " + word2)
def sayTwords2(word1: String)(word2: String) = println(word1 + " " + word2)

每个人的目的是什么？

Answer 1

第二个是咖喱，第一个不是。有关您可能选择咖喱方法的讨论，请参阅What's the rationale behind curried functions in Scala?

Answer 2

sayTwords2允许部分应用该方法。

val sayHelloAnd = sayTwords2("Hello")
sayHelloAnd("World!")
sayHaelloAnd("Universe!")

注意你也可以用同样的方式使用第一个功能。

val sayHelloAnd = sayTwords("Hello", _:String)
sayHelloAnd("World!")
sayHelloAnd("Universe!")

Answer 3

def sayTwords(word1: String, word2: String) = println(word1 + " " + word2)
def sayTwords2(word1: String)(word2: String) = println(word1 + " " + word2)

第一个包含单个参数列表。第二个包含多个参数列表。

他们在以下方面有所不同：

部分应用程序语法。观察：

scala> val f = sayTwords("hello", _: String)
f: String => Unit = <function1>

scala> f("world")
hello world

scala> val g = sayTwords2("hello") _
g: String => Unit = <function1>

scala> g("world")
hello world

前者具有位置语法的好处。因此，您可以在任何位置部分应用参数。

类型推断。 Scala中的类型推断按参数列表工作，并从左到右。因此，考虑到一个案例，人们可能会促进更好的类型推断。观察：

scala> def unfold[A, B](seed: B, f: B => Option[(A, B)]): Seq[A] = {
|   val s = Seq.newBuilder[A]
|   var x = seed
|   breakable {
|     while (true) {
|       f(x) match {
|         case None => break
|         case Some((r, x0)) => s += r; x = x0
|       }
|     }
|   }
|   s.result
| }
unfold: [A, B](seed: B, f: B => Option[(A, B)])Seq[A]

scala> unfold(11, x => if (x == 0) None else Some((x, x - 1)))
<console>:18: error: missing parameter type
      unfold(11, x => if (x == 0) None else Some((x, x - 1)))
        ^

scala> unfold(11, (x: Int) => if (x == 0) None else Some((x, x - 1)))
res7: Seq[Int] = List(11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

scala> def unfold[A, B](seed: B)(f: B => Option[(A, B)]): Seq[A] = {
|   val s = Seq.newBuilder[A]
|   var x = seed
|   breakable {
|     while (true) {
|       f(x) match {
|         case None => break
|         case Some((r, x0)) => s += r; x = x0
|       }
|     }
|   }
|   s.result
| }
unfold: [A, B](seed: B)(f: B => Option[(A, B)])Seq[A]

scala> unfold(11)(x => if (x == 0) None else Some((x, x - 1)))
res8: Seq[Int] = List(11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

这两种方法定义之间的区别

3 个答案: