scala> class B { override def foo(i: Int): Unit = {}; }
-- [E037] Declaration Error: ---------------------------------------------------
1 |class B { override def foo(i: Int): Unit = {}; }
  |                       ^
  |                       method foo overrides nothing
  |
  | longer explanation available when compiling with `-explain`
1 error found
scala> class A { def foo: Unit = {}; }
// defined class A
scala> class B extends A { override def foo(i: Int): Unit = {}; }
-- [E038] Declaration Error: ---------------------------------------------------
1 |class B extends A { override def foo(i: Int): Unit = {}; }
  |                                 ^
  |      method foo has a different signature than the overridden declaration
  |
  | longer explanation available when compiling with `-explain`
1 error found
