Kotlin Programming: The Big Nerd Ranch Guide, 2nd Edition

For the More Curious: The Safe Cast Operator

Earlier in this chapter, we introduced the as operator as a mechanism for performing casting. We also mentioned that type casting in this way is sometimes deemed unsafe and can lead to ClassCastExceptions if you perform an invalid cast when your program runs.

In addition to the as operator, there is also a safe cast operator, which is as?. as? behaves very similarly to as, but with one key difference: If you perform an invalid cast, as? returns null instead of throwing an exception. Try it out for yourself in the REPL:

Listing 15.26  Safe and unsafe casting (REPL)

5 as String
ClassCastException: class Integer cannot be cast to class String

5 as? String
null

as? is a great way ...