How to return null from a generic function in Scala?
generics, null, scala
Solution
This is because `T` could be a non-nullable type. It works when you enforce `T` to be a nullable type:
def unwrap[T >: Null](iface: Class[T]): T = null
unwrap(classOf[String]) // compiles
unwrap(classOf[Int]) // does not compile, because Int is not nullable
Problem
I am writing my own simple `javax.sql.DataSource` implementation, the only method of it I need to work is `getConnection: Connection`, but the interface inherits many other methods (which I don't need) from `javax.sql.CommonDataSource` and `java.sql.Wrapper`. So, I would like to "implement" those unneeded methods a way they wouldn't actually work but would behave an adequate way when called. For example I implement `boolean isWrapperFor(Class<?> iface)` as ``` def isWrapperFor(iface: Class[_]): Boolean = false ``` and I'd like to implement `<T> T unwrap(Class<T> iface)` as ``` def unwrap[T](iface: Class[T]): T = null ``` But the last doesn't work: the compiler reports type mismatch. Will it be correct to use `null.asInstanceOf[T]` or is there a better way? Of course I consider just throwing `UnsupportedOperationException` instead in this particular case, but IMHO the question can still be interesting.