一个比较难懂的隐式转换过程

思考一下TernaryOp.test中发生了什么.scala

object TernaryOp {
  class Ternary[T](t: T) {
    println("Ternary") 
    def is[R](bte: BranchThenElse[T,R]) = {
       println("is ... ")
       if (bte.branch(t)) bte.then(t) else bte.elze(t)
   } 
 }
  class Branch[T](branch: T => Boolean) {
    println("branch");
    def ?[R] (then: T => R) = { println("?"); new BranchThen(branch,then) } 
  }
  
  class BranchThen[T,R](val branch: T => Boolean, val then: T => R){
     println("BranchThen")
  }
  
  class Elze[T,R](elze: T => R) {
     println("Elze")
    def :: (bt: BranchThen[T,R]) = { println("::"); new BranchThenElse(bt.branch,bt.then,elze) } 
  }
  
  class BranchThenElse[T,R](val branch: T => Boolean, val then: T => R, val elze: T => R)
  
  implicit def any2Ternary[T](t: T) = new Ternary(t)
  implicit def fct2Branch[T](branch: T => Boolean) = new Branch(branch)
  implicit def fct2Elze[T,R](elze: T => R) = new Elze(elze)
  
  def test = {
     this.getClass.getSimpleName is {s: String => s.endsWith("$")} ? {s: String => s.init} :: {s: String => s}
// 等价于 test2 
   }
   def test2 = {
       this.getClass.getSimpleName is (({s: String => s.endsWith("$")} ? {s: String => s.init}) :: {s: String => s})
   }
}

对于TernaryOp.test来说，结果显示的先后顺序是
Ternary
branch
?
BranchThen
Elze
::
is ...
res36: String = TernaryOp
其中XX是一个数字，与REPL当时的状态有关。

其实只要明确is,?和::的执行顺序（关于函数（或方法，运算符的）的优先级请查阅《Programming in Scala 》第5.8节），那么就不难解读TernaryOp.test的实现。这三个函数的执行顺序依次是: ?, ::, is