Scala,模式匹配,字符串

Question

有没有办法匹配scala中的字符串,如下所示:

  def matcher(arg: String) : Expr = {
    case left :: '*' :: right => new Binary("*", left, right)
    case left :: '+' :: right => new Binary("+", left, right)
  }

哪里左右都有String类型？

Answer 1

您可以通过匹配正则表达式来实现目标.

trait Expr

case class Binary(op: String, leftOperand: String, rightOperand: String) extends Expr

val mulPattern = "(\\d*)\\*(\\d*)".r
val addPattern = "(\\d*)\\+(\\d*)".r

def matcher(arg: String) : Expr = {
  arg match {
    case mulPattern(left, right) => new Binary("*", left, right)
    case addPattern(left, right) => new Binary("+", left, right)
  }
}

def main(args: Array[String]): Unit = {
  println(matcher("1+2")) // Binary("+", "1", "2")
  println(matcher("3*4")) // Binary("*", "3", "4")
} 

Answer 2

您还可以使用提取器执行此操作：

object Mult {
  def unapply(x: String): Option[(String, String)] = x.split("\\*") match {
    case Array(a: String, b: String) => Some(a -> b)
    case _ => None
  }
}

object Add {
  def unapply(x: String): Option[(String, String)] = x.split("\\+") match {
    case Array(a: String, b: String) => Some(a -> b)
    case _ => None
  }
}

def matcher(arg: String) = arg match {
    case Mult(left, right) => Binary("*", left, right)
    case Add(left, right) => Binary("+", left, right)
    case _ => println("not matched")
 }

您可能还想为每个提取器实现 apply 方法，例如：

def apply(l: String, r: String) = s"$l*$r"

但这不是强制性的