57.scala编程思想笔记——使用特征构建系统

        欢迎转载，转载请标明出处：http://blog.csdn.net/notbaron/article/details/50447611
源码下载连接请见第一篇笔记。

 特征是如此独立且影响微小，可以将问题按照需要分解为大量的小碎片。

         例如：

package sodafountain

 

object Quantity extends Enumeration {

  type Quantity= Value

  val None,Small, Regular,

    Extra,Super = Value

}

import Quantity._

 

object Holder extends Enumeration {

  type Holder =Value

  val Bowl,Cup, Cone, WaffleCone = Value

}

import Holder._

 

trait Flavor

 

object Syrup extends Enumeration {

  case class_Val() extends Val

    with Flavor

  type Syrup =_Val

  valChocolate, HotFudge,

   Butterscotch, Caramel = _Val()

}

import Syrup._

 

object IceCream extends Enumeration {

  case class_Val() extends Val

    with Flavor

  type IceCream= _Val

  valChocolate, Vanilla, Strawberry,

    Coffee,MochaFudge, RumRaisin,

    ButterPecan= _Val()

}

import IceCream._

 

object Sprinkle extends Enumeration {

  case class_Val() extends Val

    with Flavor

  type Sprinkle= _Val

  val None,Chocolate, Rainbow = _Val()

}

import Sprinkle._

 

trait Amount {

  valquant:Quantity

}

 

trait Taste[F <: Flavor] extends Amount {

  val flavor:F

}

 

case class

Scoop(quant:Quantity, flavor:IceCream)

extends Taste[IceCream]

 

trait Topping

 

case class

Sprinkles(quant:Quantity, flavor:Sprinkle)

extends Taste[Sprinkle] with Topping

 

case class

Sauce(quant:Quantity, flavor:Syrup)

extends Taste[Syrup] with Topping

 

case class WhippedCream(quant:Quantity)

extends Amount with Topping

 

case class Nuts(quant:Quantity)

extends Amount with Topping

 

class Cherry extends Topping

注意：Flavor和Topping 都是标记特征。

在编写代码时，最基本的一条准则是越短的语句越好。

另一条同等重要的准则是消除重复代码。

         编译上述代码：

# scalac SodaFountain.scala

然后制作如下代码，可以制作一些甜点：

import com.atomicscala.AtomicTest._

import sodafountain._

import Quantity._

import Holder._

import Syrup._

import IceCream._

import Sprinkle._

 

case class

Scoops(holder:Holder, scoops:Scoop*)

 

val iceCreamCone = Scoops(

  WaffleCone,

  Scoop(Extra,MochaFudge),

  Scoop(Extra,ButterPecan),

  Scoop(Extra,IceCream.Chocolate))

 

iceCreamCone is "Scoops(WaffleCone," +

"WrappedArray(Scoop(Extra,MochaFudge), " +

"Scoop(Extra,ButterPecan), " +

"Scoop(Extra,Chocolate)))"

 

case class MadeToOrder(

 holder:Holder,

 scoops:Seq[Scoop],

 toppings:Seq[Topping])

 

val iceCreamDish = MadeToOrder(

  Bowl,

  Seq(

   Scoop(Regular, Strawberry),

   Scoop(Regular, ButterPecan)),

 Seq[Topping]())

 

iceCreamDish is "MadeToOrder(Bowl," +

"List(Scoop(Regular,Strawberry), " +

"Scoop(Regular,ButterPecan)),List())"

 

case class Sundae(

  sauce:Sauce,

 sprinkles:Sprinkles,

 whipped:WhippedCream,

  nuts:Nuts,

 scoops:Scoop*) {

  valholder:Holder = Bowl

}

 

val hotFudgeSundae = Sundae(

 Sauce(Regular, HotFudge),

 Sprinkles(Regular, Sprinkle.Chocolate),

 WhippedCream(Regular), Nuts(Regular),

 Scoop(Regular, Coffee),

 Scoop(Regular, RumRaisin))

 

hotFudgeSundae is "Sundae(" +

 "Sauce(Regular,HotFudge)," +

  "Sprinkles(Regular,Chocolate),"+

 "WhippedCream(Regular),Nuts(Regular)," +

 "WrappedArray(Scoop(Regular,Coffee), " +

 "Scoop(Regular,RumRaisin)))"

其中Scoops是基本的实现，利用它可以创建一个冰淇淋筒或一盘冰淇淋。