Scala 中置, 前置, 后置操作符

1MyNumber(10).+(MyNumber(20))   //标准调用格式
2MyNumber(10) + MyNumber(20)    //只有一个参数时, 不用点, 不用括号

1def plus(added: Int) = MyNumber(this.value + added)

1MyNumber(10) plus 20  //而可不必写成  MyNumber(10).plus(20)

1actualList must have size 10

1case class MyNumber(value: Int) {
2  def -- = MyNumber(this.value -1)
3}

1MyNumber(10).--  //这是标准格式
2MyNumber(10) --  //无参方法的约定格式

1def --() = MyNumber(this.value -1)  //Empty-paren 方法
2....
3MyNumber(10) --      //Warning: Empty-paren method accessed as parameterless
4MyNumber(10).--     //Warning: Empty-paren method accessed as parameterless
5MyNumber(10).--()

1a toString  //而不用写成 a.toString() 或 a.toString
2a mkString

1case class MyNumber(value: Int) {
2  def unary_+ = MyNumber(this.value + 1)
3}

1MyNumber.unary_+  //标准调用格式, 或 MyNumber unary_+
2+MyNumber(10)    //实际就调用了 unary_+ 方法

1def unary_++ = MyNumber(this.value + 1)
2....
3//++MyNumber(10)  //这是无效的, 尝试不会是徒劳的. 只能显式的用下面两种方式调用
4MyNumber(10).unary_++
5MyNumber(10) unary_++

 1import scala.language.postfixOps
 2
 3case class MyNumber(value: Int) {
 4
 5 def +(that: MyNumber) = MyNumber(this.value + that.value)
 6
 7 def ++ = MyNumber(this.value + 1) //parameterless
 8
 9 // def -- = MyNumber(this.value - 1) //recommended
10 def --() = MyNumber(this.value - 1) //Warning: Empty-paren, not recommended for no side-effect method
11
12 def unary_- = MyNumber(-this.value)
13}
14
15object Main extends App {
16
17 println("Infix: " + (MyNumber(10) + MyNumber(20))) //recommended
18 println(MyNumber(10).+(MyNumber(20))) //regular method calling style
19
20 println("Postfix1: " + (MyNumber(10) ++)) //recommended
21 println(MyNumber(10).++) //regular method calling style
22
23 // MyNumber(10).++() //Compilation error: Application does not take parameters
24
25 println("Postfix2: " + (MyNumber(10) --)) //Warning: Empty-paren method accessed as parameterless
26 println((MyNumber(10).--)) //Warning: Empty-paren method accessed as parameterless
27 println(MyNumber(10).--()) //regular method calling style
28
29 println("Prefix: " + -MyNumber(10))
30
31 println(MyNumber(10).unary_-)
32 println((MyNumber(10) unary_-))
33}