Blog Scala - unapply http://blog.joecwu.com/2015/07/scala-unapply-extraction-method.html

blog-Scala-unapply-1.scala

case class GetArticleRequest(id:String,country:String,language:String)
 
def parseRequest(queryStr:String) = {
    // parse arguments
    val args = queryStr.split('&') map { str =>
      val pair = str.split('=')
      (pair(0) -> pair(1))
    } toMap
    // get 'id','country','language' and gen GetArticleRequest object
    val resp = for{
      id <- args.get("id")
      country <- args.get("country")
      language <- args.get("language")
    }yield(GetArticleRequest(id,country,language))
    resp
}
 
object TestApp {
  def run {
    val queryString = "id=abc&country=TW&language=zh"
    
    // Extract value
    val request = parseRequest(queryString).getOrElse(thrown Exception("invalid request"))
    println(s"id:[${request.id}], country:[${request.country}], language:[${request.language}]")
  
    // Pattern match
    val request2 = parseRequest(queryString).getOrElse(thrown Exception("invalid request"))
    request2 match {
      case GetArticleRequest(id,country,language) => println(s"id:[$id], country:[$country], language:[$language]")
    }
  }
}

blog-Scala-unapply-2.scala

object GetArticleRequest {
  def unapply(queryStr:String): Option[(String, String, String)] = {
    // parse arguments
    val args = queryStr.split('&') map { str =>
      val pair = str.split('=')
      (pair(0) -> pair(1))
    } toMap
    // get 'id','country','language'
    val resp = for{
      id <- args.get("id")
      country <- args.get("country")
      language <- args.get("language")
    }yield((id,country,language))
    resp
  }
}
 
object TestApp {
  def run {
    // Extract value directly
    val GetArticleRequest(id,country,language) = "id=abc&country=TW&language=zh"
    println(s"id:[$id], country:[$country], language:[$language]")
    
    // Pattern match
    "id=abc&country=TW&language=zh" match {
      case GetArticleRequest(id,country,language) => println(s"id:[$id], country:[$country], language:[$language]")
    }
  }
}