Match Self-Recursive Type in Macro

Question

I guess self-recursive types are well-known in Scala. A nice intro can be found at here. The following piece of code is taken from that page:

trait Doubler[T <: Doubler[T]] { self: T =>
  def double: T
}

In Scala 3 Macros, we can match on types, introduced with examples on this page (right before "Quote types patterns" Section). However, I still don't know how to match self-recursive types. Any idea?

Imagine that I have the following method:

def doSomething[T <: Doubler[T]](value: T): Unit = { ... }

And the following macro:

  inline def myMacro[A](inline value: A): Unit = ${ myMacroImpl('value) }

  private def myMacroImpl[A: Type](value: Expr[A])(using q: Quotes): Expr[Unit] =
    import q.reflect.*
    value match
      case '{ $x: /*help-me*/ } => '{ doSomething($x) }
      case _ => // irrelevant

How should I fix the first case to make the code even compile?

Match Self-Recursive Type in Macro

0 Answers