scala 语法：连接符"~"和 at符“@”

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本文深入解析Scala中的连接符~和at符@的用法。通过具体示例代码展示了如何使用这些符号进行表达式解析及模式匹配操作。

一、scala 连接符~解析

import scala.util.parsing.combinator._

object ArithExpr extends JavaTokenParsers {
  

  def expr: Parser[Any] = {

   
     log(term)("加减法表达式  term") ~ rep("+" ~ log(term)("加法 term")  | "-"~ log(term)("减法  term") )
  }
  def term: Parser[Any] = log(factor)("乘除法表达式   factor")  ~ rep("*" ~ log(factor)("乘法 factor") | "/" ~ log(factor)("除法  factor"))
  def factor: Parser[Any] = (wholeNumber | decimalNumber | floatingPointNumber) | "(" ~ log(expr)("factor expr") ~ ")"

  def main(args: Array[String]) {

  
    println(parseAll(expr, "(1*2)* 5"))
  }
}

运行结果如下

"C:\Program Files\Java\jdk1.8.0_65\bin\java" -Didea.launcher.port=7532 "-Didea.launcher.bin.path=C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 15.0.2\bin" -......" com.intellij.rt.execution.application.AppMain ArithExpr
trying 加减法表达式 term at scala.util.parsing.input.CharSequenceReader@1fd3711
trying 乘除法表达式 factor at scala.util.parsing.input.CharSequenceReader@1fd3711
trying factor expr at scala.util.parsing.input.CharSequenceReader@f9b8bc
trying 加减法表达式 term at scala.util.parsing.input.CharSequenceReader@f9b8bc
trying 乘除法表达式 factor at scala.util.parsing.input.CharSequenceReader@f9b8bc
乘除法表达式 factor --> [1.3] parsed: 1
trying 乘法 factor at scala.util.parsing.input.CharSequenceReader@146e1f4
乘法 factor --> [1.5] parsed: 2
加减法表达式 term --> [1.5] parsed: (1~List((*~2)))
factor expr --> [1.5] parsed: ((1~List((*~2)))~List())
乘除法表达式 factor --> [1.6] parsed: (((~((1~List((*~2)))~List()))~))
trying 乘法 factor at scala.util.parsing.input.CharSequenceReader@144fc66
乘法 factor --> [1.9] parsed: 5
加减法表达式 term --> [1.9] parsed: ((((~((1~List((*~2)))~List()))~))~List((*~5)))
[1.9] parsed: (((((~((1~List((*~2)))~List()))~))~List((*~5)))~List())
Process finished with exit code 0

二、Scala at符@

scala中 @ 除了是注解以及抽取XML的属性功能以外 , 还有一个功能就是模式匹配中匹配类似 some的值

  * Created by admin on 2016/12/28.
  */
object test6 {
  def main(args: Array[String]) {

   val d@(c@Some(a), Some(b)) = (Some(1), Some(2))
    println(d)
    println(c)
    println(a)
    println(b)

    println()
     (Some(1), Some(2)) match {
      case d@(c@Some(a), Some(b)) => println(a, b, c, d)
    }

    println()
    println()
    for (x @ Some(y) <- Seq(None, Some(1))) println(x, y)
    val List(x, xs@_*) = List(1, 2, 3)
    println(x)
    println(xs)
    println()
    val o: Option[Int] = Some(2)
    o match {
      case Some(x) => println(x)
      case None =>
    }
    o match {
      case x@Some(_) => println(x)
      case None =>
    }


  }
}

运行结果

"C:\Program Files\Java\jdk1.8.0_65\bin\java" -Didea.launcher.port=7537 "-Didea.launcher.bin.path=.......r" com.intellij.rt.execution.application.AppMain test6
(Some(1),Some(2))
Some(1)
1
2

(1,2,Some(1),(Some(1),Some(2)))

(Some(1),1)
1
List(2, 3)

2
Some(2)

Process finished with exit code 0