variances.scala

来自「JAVA 语言的函数式编程扩展」· SCALA 代码 · 共 62 行

package test

trait Vector[+A] {
  def append(x: Vector[A]): Vector[A] 
  private[this] def append3(x: Vector[A]): Vector[A] = append(x)
}

class C[T]

object Covariant {
  class Foo[+A] {
    private[this] var a : A = _
    def getA : A = a
    private[this] def setA(a : A) = this.a = a 
    
    object Baz extends C[A]
    trait Convert[B] {
      def b2a(b : B) : A
      def doit(b : B) = setA(b2a(b))
    }
  }
  class Foo2[+A] {
    private[this] var a : A = _
    def getA : A = a
    private[this] def setA(a : A) = this.a = a 
    
    {
      trait Convert[B] {
        def b2a(b : B) : A
        def doit(b : B) = setA(b2a(b))
      }
      ()
    }
  }
  class Foo3[+A] {
    private[this] var a : A = _
    def getA : A = a
    private[this] def setA(a : A) = this.a = a 
    
    private[this] trait Convert[B] {
      def b2a(b : B) : A
      def doit(b : B) = setA(b2a(b))
    }
  }
  abstract class AbstractTest {
    val a : Foo[AnyRef]
    val c = new a.Convert[Int] {
      def b2a(b : Int) : AnyRef = "hello"
    }
    val b : Int = 42
  }
  class Test extends AbstractTest {
    val a : Foo[java.lang.Character] = new Foo[java.lang.Character]
  }
  def main(args : Array[String]) {
    val test = new Test
    test.c.doit(test.b)
    val x : java.lang.Character = test.a.getA
    Console.println("XXX " + x)
  }
}