如何使用地图返回 Double

Question

I try to making token lexical analyzer and I want return Double type using map in scala

    var m = Map[String,Double]()
    def parseItem(tok: Tokenizer): Double = {
    val startPos = tok.tokenPos
    val t = tok.token
    tok.next()
    //(other codes)
    else if (t.isIdentifier) {
      var t1 = tok.token
      if(t1.text == "=") {
        tok.next()
        var t2 = tok.token
        if(t2.isNumber) {
          m += (t.text -> t2.number)
          println("Idenrifier sorted :" + t.text)
          0
        }else if(t2.isIdentifier && m.get(t2.text) == None){
            println("Error!!! RHS is Wrong identifier!!!")
            throw new SyntaxError(startPos, "expected number, identifier, or '('")
        }else{
          m += (t.text -> m.get(t2.text))
          println("Idenrifier sorted :" + t.text)
          0
        }
      }else{
          m.get(t.text)
      }

the error code is :Option[Double] I think return type is Double But I can't understanding this error

Answer 1

  m.get(t.text) is of type Option[Double] 

You can use the apply method of the Map but keep in mind that the apply method returns the value associated with a given key directly, without wrapping it in an Option. If the key is not defined in the map, an exception is raised.

You can use m(t.text) or m.apply(t.text)

Or you can use m getOrElse (t.text, defaultValue) ,which returns the value associated with key t.text in the m map , or the defaultValue if not found.