如何从抽象类获得所有扩展类？How to get all extended classes from abstract class

https://cn.community.intersystems.com/post/%E5%A6%82%E4%BD%95%E4%BB%8E%E6%8A%BD%E8%B1%A1%E7%B1%BB%E8%8E%B7%E5%BE%97%E6%89%80%E6%9C%89%E6%89%A9%E5%B1%95%E7%B1%BB%EF%BC%9Fhow-get-all-extended-classes-abstract-class