SerializationProxy

class SerializationProxy[A](var coll: Stream[A]) extends Serializable

This serialization proxy is used for Streams which start with a sequence of evaluated cons cells. The forced sequence is serialized in a compact, sequential format, followed by the unevaluated tail, which uses standard Java serialization to store the complete structure of unevaluated thunks. This allows the serialization of long evaluated streams without exhausting the stack through recursive serialization of cons cells.

Source:
Stream.scala
class Object
trait Matchable
class Any