Dart can as well. In fact, I think that the whole type spec in AtScript is based on Dart. Edit: Quote from the doc you linked: "This runtime type system is mod

Dart can as well. In fact, I think that the whole type spec in AtScript is based on Dart. Edit: Quote from the doc you linked: "This runtime type system is modeled after Dart’s runtime type assertion. Dart users working on large scale applications point out that optional types and runtime type assertions work well in practice."