/ProgrammingInScala

Programming In Scala 3rd Examples.《Scala编程》第三版代码

Primary LanguageScala

Programming In Scala

脚本运行方式:

scala -nc hello.scala

类运行方式:

➜  ch04 git:(master) ✗ scalac ChecksumAccumulator.scala Summer.scala
➜  ch04 git:(master) ✗ scala ch04.Summer hello scala                
hello: -20
scala: -4

1. A Scalable Language

语言命名

2. First Steps in Scala

写点脚本

3. Next Steps in Scala

使用List,Tuple,Set,Map

读文件

4. Classes and Objects

5. Basic Types and Operations

6. Functional Objects

7. Built-in Control Structures

8. Functions and Closures

9. Control Abstractions

10. Composition and Inheritance

11. Scala's Hierarchy

12. Traits

13. Packages and Imports

14. Assertions and Tests

15. Case Classes and Pattern Matching

16. Working with Lists

17. Working with other Collections

18. Mutable Objects

19. Type Parameterization

20. Abstract Members

scala> trait Abstract {
     |   type T
     |
     |   def transform(x: T): T
     |
     |   val initial: T
     |
     |   var current: T
     | }
defined trait Abstract

scala> class Concrete extends Abstract {
     |   type T = String
     |
     |   def transform(x: String) = x + x
     |
     |   val initial = "hi"
     |   var current = initial
     | }
defined class Concrete

scala>

scala> println(new Concrete().transform("vonzhou"))
vonzhouvonzhou

21. Implicit Conversions and Parameters

scala.Int:

  import scala.language.implicitConversions
  implicit def int2long(x: Int): Long = x.toLong
  implicit def int2float(x: Int): Float = x.toFloat
  implicit def int2double(x: Int): Double = x.toDouble

Predef:

 implicit final class ArrowAssoc[A](private val self: A) extends AnyVal {
    @inline def -> [B](y: B): Tuple2[A, B] = Tuple2(self, y)
    def →[B](y: B): Tuple2[A, B] = ->(y)
  }

22. Implementing Lists

2个子类：:: 和 Nil

covariant

val xs = List(1,2,3)
var ys:List[Any] = xs
println(ys)

List定义了3个抽象方法：

 def isEmpty: Boolean
  def head: A
  def tail: List[A]

:: 方法的参数类型有一个lower bound，交互模式下运行：

scala> abstract class Fruit
defined class Fruit

scala> class Apple extends Fruit
defined class Apple

scala> class Orange extends Fruit
defined class Orange

scala> val apples = new Apple :: Nil
apples: List[Apple] = List(Apple@1224e1b6)

scala> val fruits = new Orange :: apples
fruits: List[Fruit] = List(Orange@61d09475, Apple@1224e1b6)

ListBuffer的实现：

  def += (x: A): this.type = {
    if (exported) copy()
    if (isEmpty) {
      last0 = new :: (x, Nil)
      start = last0
    } else {
      val last1 = last0
      last0 = new :: (x, Nil)
      // 注意 :: 类构造器参数 tl 是var
      last1.tl = last0
    }
    len += 1
    this
  }

The design of Scala's List and ListBuffer is quite similar to what's done in Java's pair of classes String and StringBuffer.

23. For Expression Revisited

for 表达式最终都会被scala 编译器转换成map, flatMap, withFilter。

24. Collections in depth