鸭子类型：“当看到一只鸟走起来像鸭子、游泳起来像鸭子、叫起来也像鸭子，那么这只鸟就可以被称为鸭子。”

一般在动态语言里面才有，因为静态语言是强类型的，会在编译期检查类型，很难实现。但是Scala作为一门static type语言，居然支持，不得不说Scala确实很强大。直接上code

package testscala

object StructuralTyping extends App {
  def quacker(duck: {def quack(value: String): String}) {
    println(duck.quack("Quack"))
  }

  object BigDuck {
    def quack(value: String) = {
      value.toUpperCase
    }
  }

  object SmallDuck {
    def quack(value: String) = {
      value.toLowerCase
    }
  }

  object IamNotReallyADuck {
    def quack(value: String) = {
      "prrrrrp"
    }
  }

  quacker(BigDuck)
  quacker(SmallDuck)
  quacker(IamNotReallyADuck)

  //  object NoQuaker {
  //  }
  //
  //  quacker(NoQuaker) // 编译错误！！！！

  val x = new AnyRef {
    def quack(value: String) = {
      "No type needed " + value
    }
  }
  quacker(x)

}

Why scala uses reflection to call method on structural type?

Why No One Uses Scala’s Structural Typing

Ref

1. http://en.wikibooks.org/wiki/Scala/Structural_Typing

2. http://java.dzone.com/articles/duck-typing-scala-structural

3. http://www.draconianoverlord.com/2011/10/04/why-no-one-uses-scala-structural-typing.html

4. http://stackoverflow.com/questions/8539422/why-scala-uses-reflection-to-call-method-on-structural-type

Scala Structural Typing结构类型

原文：http://my.oschina.net/magicly007/blog/313863