Nevermind - sorry for the clutter.
For those who are apparently as dense as I am, this can be roughly
accomplished via Template specialization:
class Fruit {}
class Apple : Fruit {}
class Celery {}
void mustBeFruit(T : Fruit)() {
writeln(T.classinfo.name);
}
void main() {
mustBeFruit!(Apple)(); // Ok
mustBeFruit!(Celery)(); // Does not compile
}