Match expression: Test the type of a variable

 Following 'case' syntax is used to test the type of a variable. 

Syntax

case <identifier> : <type> => {.....}

scala> var x : Any = 10
var x: Any = 10

scala> var result = x match{
     |   case someVar:Integer => {"Integer"}
     |   case someVar:String => {"String"}
     |   case someVar:AnyRef => {"AnyRef"}
     |   case _ =>{"Any"}
     | }
var result: String = Integer

scala> print(result)
Integer

You can even use _ as a placeholder for the identifier.

scala> var x:Any = "Hello World"
var x: Any = Hello World

scala> var result = x match{
     |   case _:Integer => {"Integer"}
     |   case _:String => {"String"}
     |   case _:AnyRef => {"AnyRef"}
     |   case _ =>{"Any"}
     | }
var result: String = String

Find another example.

scala> var x:Any = new Object
var x: Any = java.lang.Object@c725dfa

scala> var result = x match{
     |   case _:Integer => {"Integer"}
     |   case _:String => {"String"}
     |   case _:AnyRef => {"AnyRef"}
     |   case _ =>{"Any"}
     | }
var result: String = AnyRef

scala> print(result)
AnyRef

Variable whose type you are matching must be a base type, else scrutinee error will be thrown by Scala.

scala> var x:Integer = 10
var x: Integer = 10

scala> var result = x match{
     |           case someVar:Integer => {"Integer"}
     |           case someVar:String => {"String"}
     |           case someVar:AnyRef => {"AnyRef"}
     |           case _ =>{"Any"}
     |      }
     | 
                 case someVar:String => {"String"}
                              ^
On line 3: error: scrutinee is incompatible with pattern type;
        found   : String
        required: Integer

As you see in the above example, I define a variable ‘x’ is of type integer, but I am trying to match x with incompatible type String, so Scala compiler throws error.

 

To resolve the above error, define variable ‘x’ with type Any.

scala> var x:Any = 10
var x: Any = 10

scala> var result = x match{
     |           case someVar:Integer => {"Integer"}
     |           case someVar:String => {"String"}
     |           case someVar:AnyRef => {"AnyRef"}
     |           case _ =>{"Any"}
     |      }
var result: String = Integer

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