CODEWITHSUNDEEP
scalascala-collections
Kevin Thoriya
Kevin Thoriya

Reputation: 13

Scala - Iterate a Any variable which contains List()

scala > 
       var a : Any = List(1,2,3,4,5,6,7,8,9,0)

I want to iterate variable a. as it print 

1
2
3
4
5
6
7
8
9
0

Upvotes: 1

Views: 150

Answers (2)

Mario Galic
Mario Galic

Reputation: 48410

Collections such as List are usually "iterated" over using map/foreach higher-order methods, however the reason we cannot call them directly on a is because compiler thinks the type of a is Any as we explicitly specified type annotation a: Any. 

 var a: Any            =    List(1,2,3,4,5,6,7,8,9,0)
         |                    | 
 compile-time type          runtime class

Any does not provide map/foreach API so the best we can do is it to perform a runtime cast of reference a to class List[_] like so

if (a.isInstanceOf[List[_]]) a.asInstanceOf[List[_]].foreach(println) else ???

which can be equivalently sugared using pattern match

a match {
  case value: List[_] => value.foreach(println)
  case _ => ???
}

As a side-note, due to type erasure we can only check the "top-level" class List and not, for example, List[Int], hence a.isInstanceOf[List[Int]] is a bit misleading so I prefer expressing it a.isInstanceOf[List[_]].

Upvotes: 2

Andronicus
Andronicus

Reputation: 26046

Just use pattern matching:

a match {
    case l: List[Int] => l.foreach(println)
}

P.S.: As @IvanStanislavciuc cleverly notices, there is a warning:

warning: non-variable type argument Int in type pattern List[Int] (the underlying of List[Int]) is unchecked since it is eliminated by erasure 1

It's because of type erasure, but List needs a type parameter, so you can as well pass Any instead of Int.

Upvotes: 2

Related Questions