D语言 中的 this指针函数

import std.stdio;

class Box { 
   public: 
      //构造函数定义
      this(double l=2.0, double b=2.0, double h=2.0) { 
         writeln("Constructor called."); 
         length=l;
         breadth=b; 
         height=h; 
      }
         
      double Volume() { 
         return length * breadth * height; 
      }

      int compare(Box box) { 
         return this.Volume() > box.Volume(); 
      }

   private: 
      double length;     //长
      double breadth;    //宽
      double height;     //高
}
  
void main() { 
   Box Box1=new Box(3.3, 1.2, 1.5);    //实例化box1
   Box Box2=new Box(8.5, 6.0, 2.0);    //实例化box2
   
   if(Box1.compare(Box2)) { 
      writeln("Box2 is smaller than Box1"); 
   } else { 
      writeln("Box2 is equal to or larger than Box1"); 
   }
}