At the risk of being that guy who always brings up rust: enum Process { Invalid, Terminated, Pid(libc::pid_t), } There would

At the risk of being that guy who always brings up rust: enum Process { Invalid, Terminated, Pid(libc::pid_t), } There would be no way you could pass instances of the first two enum variants to kill(). Rust is of course not the only language where you can express something like this; e.g. in Scala2: sealed trait Process object Process ( case object Invalid extends Process case object Terminated extends Process case class Pid(pid: Int) extends Process } Does D have algebraic data types? Only allowing enums to be represented by integers is a language weakness.