scala-协变和逆变

class GaoJi
 
class ZhongJi extends GaoJi
 
//协变===========================
class Card[+T]
 
val cgaoji = new Card[GaoJi]
val czhongji = new Card[ZhongJi]
 
//协变之后Card[ZhongJi]犹如继承了Card[GaoJi]
def test(card: Card[GaoJi]): Unit = {
  println(123)
}
 
test(cgaoji)
test(czhongji)
 
//逆变===========================
class Card1[-T]
 
val cgaoji1 = new Card1[GaoJi]
val czhongji1 = new Card1[ZhongJi]
 
//逆变之后Card[GaoJi]犹如Card[ZhongJi]的父类也可被接收
def test1(card: Card1[ZhongJi]): Unit = {
  println(678)
}
 
test1(cgaoji1)
test1(czhongji1)