Welcome to Scala 3.5.1-RC2 (21.0.4, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                                             
scala> trait A; trait B
// defined trait A
// defined trait B
                                                                                                                                             
scala> def x: A with B = ???
1 warning found
-- [E003] Syntax Warning: ------------------------------------------------------
1 |def x: A with B = ???
  |         ^^^^
  |         with as a type operator has been deprecated; use & instead
  |
  | longer explanation available when compiling with `-explain`
def x: A & B
                                                                                                                                             
scala> def x: A & B = ???
def x: A & B