scala 逆变和协变的判断

break.scala

import scala.util.control.Breaks._
object Continued extends scala.util.control.Breaks {}
import Continued.{break=>continue, breakable=>continuing}

// Now every time you need it:
breakable{ for (i <- 1 to 10) continuing {
  if ((i%2)==0) continue
  if (i>3) break
  println(i)
}}

covariance.scala

//
trait  T[-A,+B] {val name:B  ;def say(a:A,b:B=>A):B = name}

//说明：
/*
因为Function1[-P,+R] ,所以方法参数是-值，而返回值和参数类型是+值。
当给方法的类型标上+/-后，需要符合[-A,+B]:
so, name:B+ -> +B
    a:A- -> -A
    b:(B-=>A+)- => +B ， -A
都满足了。 

*/