scala - Scala 中 2 个集合的叉积

Question

val cross = (for (x<-setA; y<-setB) yield (x,y))

val cross2 = (setA flatMap (x => setB map ((x,_)))

有没有更优雅的方法来使用交叉产品运算符或类似的方法来做到这一点？
例如:

val cross3 = setA cross setB

Answer 1

import scala.collection.Set

class
Crossable[E1](es1: Traversable[E1])
{
    def
    ×[E2](es2: Traversable[E2]): Traversable[(E1, E2)] =
      for (e1 <- es1; e2 <- es2) yield (e1, e2)

    def
    cross[E2](es2: Traversable[E2]): Traversable[(E1, E2)] =
      for (e1 <- es1; e2 <- es2) yield (e1, e2)
}


object
Crossable
{
    implicit
    def
    trav2Crossable[E1](es1: Traversable[E1]): Crossable[E1] =
        new Crossable[E1](es1)
}


object
CrossableTest
{
    def
    main(args: Array[String]): Unit = {
        import Crossable.trav2Crossable

        val es1 = Set(1, 2, 3)
        val es2 = List("a", "b", "c")

        (es1 × es2) foreach(printf("  %s%n", _))
    }
}

% scala -cp . CrossableTest
  (1,c)
  (2,b)
  (3,a)
  (2,a)
  (1,a)
  (3,b)
  (3,c)
  (1,b)
  (2,c)