Failed to convert `A with B` to `A`

[Atry]

Welcome to Scala 2.12.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_152).
Type in expressions for evaluation. Or try :help.

scala> type A = {
     |   def self: Some[Any]
     | }
defined type alias A

scala> type B = {
     |   def self: Option[String]
     | }
defined type alias B

scala> def convert(ab: A with B): A = ab
<console>:13: error: type mismatch;
 found   : A with B
 required: A
    (which expands to)  AnyRef{def self: Some[Any]}
       def convert(ab: A with B): A = ab
                                      ^

[SethTisue]

Starting dotty REPL...
scala> type A = { def self: Some[Any] } 
// defined alias type A = Object{self: : Some[Any]}
scala> type B = { def self: Option[String] } 
// defined alias type B = Object{self: : Option[String]}
scala> def convert(ab: A with B): A = ab 
def convert(ab: A & B): A

[joroKr21]

with is not true intersection in Scala 2:

scala> trait A { def self: Some[Any] } 
defined trait A

scala> trait B { def self: Option[String] } 
defined trait B

scala> def convert(ab: A with B) = ab.self
convert: (ab: A with B)Option[String]

Dotty:

scala> trait A { def self: Some[Any] } 
// defined trait A
scala> trait B { def self: Option[String] }  
// defined trait B
scala> def convert(ab: A with B) = ab.self 
def convert(ab: A & B): Some[Any] & Option[String]