Hi Brieuc, congrats for this nice article! As discussed in contributors.scala-lang.org/t/is-f-bound-polymorp… F-bounded polymorphism should most of the time be replaced by a simple minded Typeclass. In your case, this would give the following code (Scala 3 syntax):

trait Info[T, InfoType]: extension (infoType: InfoType) def update(t: T): InfoType

trait Memory[T]

case class Foo(foo: String) case class Bar(foo: Foo, foos: List[Foo])

case class FooInfo(fooMemory: Memory[String]): def update(foo: Foo): FooInfo = ??? object FooInfo: given Info[Foo, FooInfo] with extension (fooInfo: FooInfo) def update(foo: Foo): FooInfo = fooInfo.update(foo)

case class BarInfo( fooInfo: FooInfo, foosInfo: ListInfo[Foo, FooInfo] ): def update(bar: Bar): BarInfo = ???

object BarInfo: given Info[Bar, BarInfo] with extension (barInfo: BarInfo) def update(bar: Bar): BarInfo = barInfo.update(bar)

case class ListInfo[T, InfoType]( infos: List[InfoType] )(using Info[T, InfoType]): def update(listInfo: List[T]): ListInfo[T, InfoType] = ??? def updateInfoAtIndex(index: Int, t: T): ListInfo[T, InfoType] = val updatedInfo = infos(index).update(t) copy(infos = infos.updated(index, updatedInfo))