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import reflect.{ClassTag, classTag}
// abstract types and extractors, oh my!
trait TypesAPI {
trait Type
type TypeRef <: Type
val TypeRef: TypeRefExtractor; trait TypeRefExtractor {
def apply(x: Int): TypeRef
def unapply(x: TypeRef): Option[(Int)]
}
// just for illustration, should follow the same pattern as TypeRef
case class MethodType(n: Int) extends Type
}
// user should not be exposed to the implementation
trait TypesUser extends TypesAPI {
def shouldNotCrash(tp: Type): Unit = {
tp match {
case TypeRef(x) => println("TypeRef")
case MethodType(x) => println("MethodType")
case _ => println("none of the above")
}
}
}
trait TypesImpl extends TypesAPI {
object TypeRef extends TypeRefExtractor // this will have a bridged unapply(x: Type) = unapply(x.asInstanceOf[TypeRef])
case class TypeRef(n: Int) extends Type // this has a bridge from TypesAPI#Type to TypesImpl#TypeRef
// --> the cast in the bridge will fail because the pattern matcher can't type test against the abstract types in TypesUser
}
trait Foos {
trait Bar
type Foo <: Bar
trait FooExtractor {
def unapply(foo: Foo): Option[Int]
}
val Foo: FooExtractor
}
trait RealFoos extends Foos {
class Foo(val x: Int) extends Bar
object Foo extends FooExtractor {
def unapply(foo: Foo): Option[Int] = Some(foo.x)
}
}
trait Intermed extends Foos {
def crash(bar: Bar): Unit =
bar match {
case Foo(x) => println("Foo")
case _ => println("Bar")
}
}
object TestUnappStaticallyKnownSynthetic extends TypesImpl with TypesUser {
def test() = {
shouldNotCrash(TypeRef(10)) // prints "TypeRef"
shouldNotCrash(MethodType(10)) // prints "MethodType"
}
}
object TestUnappDynamicSynth extends RealFoos with Intermed {
case class NotAFoo(n: Int) extends Bar
def test() = {
crash(NotAFoo(10))
crash(new Foo(5))
}
}
object Test extends App {
TestUnappStaticallyKnownSynthetic.test()
TestUnappDynamicSynth.test()
}
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