Apologies for shattering your hopes. I have spent a long time thinking about ways to do that, and they all end up being highly invasive to the language, arguably more invasive than generics. Dart just went through a big transition to add non-nullable types and other type safety improvements, and it was a huge multi-year project. And they started out in a better place, since they have the concept of constructors in the first place. Never say never, but it’s not a high priority.