struct S {}

let optional: Optional<S> = Bool.random() ? S?.none : S?.some(S()) // OK

switch optional {
case nil: // OK
  print("It's nil")
case _?: // OK
  print("It's not nil")
}

switch optional {
case Optional<S>.none: // OK
  print("It's nil")
case Optional<S>.some: // OK
  print("It's not nil")
}

switch optional {
case S?.none: // Error: Operator function '~=' requires that 'S' conform to 'Equatable'
  print("It's nil")
case S?.some: // Error: Expression pattern of type '(S) -> Optional<S>' cannot match values of type 'Optional<S>'
              // Error: operator function '~=' requires that 'S' conform to 'Equatable'
  print("It's not nil")
}