是否在scala中应用并取消应用构造函数

class MyClass(arg: String) {
  def apply(n: Int):String = arg*n
}

val mc = new MyClass("blah")
mc.apply(2)  // res0: String = blahblah
mc(3)        // res1: String = blahblahblah

您经常会在配对对象中看到apply()用作工厂方法.

object MyClass {
  def apply(s: String): MyClass = new MyClass(s)
}
val mc = MyClass("bliss")  // call the object's apply() method

但是,这只是一个方便的惯例,而不是要求.

unapply()(和unapplySeq())的不同之处在于,只要您尝试在类实例上进行模式匹配,就会“静默”调用它.

class MyClass(val arg: String) {}
object MyClass {
  def unapply(x: MyClass): Option[String] = Some(x.arg)
}
val mc = new MyClass("bland")
mc match {
  case MyClass(s) => println(s"got $s")  // output: "got bland"
  case _          => println("not")
}