If I create a class in Scala, does it implicitly extends AnyVal, AnyRef or both?

Question

If I write a class in Scala, does it automatically extends AnyVal, AnyRef or both?

Answer 1

If I write a class in Scala, does it automatically extends AnyVal, AnyRef or both?

It should be obvious that it cannot automatically extend both because a Scala class can only extend one class, not two.

It should also be obvious that it cannot automatically extend AnyVal because classes that extend AnyVal must obey some specific restrictions which cannot, in general, be satisfied by any random class.

Therefore, the only sensible way it could work is that a class automatically extends AnyRef.

However, we don't have to use common sense, we don't have to use our brains at all, we can just look into the Scala Language Specification [bold emphasis mine]:

5.3 Class Definitions

The extends clause extends sc with mt_1 with … with mt_m can be omitted, in which case extends scala.AnyRef is assumed.