D语言抽象函数

import std.stdio; 
import std.string; 
import std.datetime; 

abstract class Person { 
   int birthYear, birthDay, birthMonth; 
   string name; 

   int getAge() { 
      SysTime sysTime = Clock.currTime(); 
      return sysTime.year - birthYear; 
   } 
   abstract void print(); 
}
class Employee : Person { 
   int empID;  

   override void print() { 
      writeln(The employee details are as follows:); 
      writeln(Emp ID: , this.empID); 
      writeln(Emp Name: , this.name); 
      writeln(Age: ,this.getAge); 
   } 
} 

void main() { 
   Employee emp = new Employee(); 
   emp.empID = 101; 
   emp.birthYear = 1980; 
   emp.birthDay = 10; 
   emp.birthMonth = 10; 
   emp.name = Emp1; 
   emp.print(); 
}