this指標


在D中每個物件都有通過一個名為this指標,這個指標存取它自己的地址。this 指標是一個隱含的引數,所有的成員函式。因此,一個成員函式內,this 可以用來指呼叫物件。

讓我們試試下面的例子就明白了this指標的概念:

import std.stdio;

class Box
{
   public:
      // Constructor definition
      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;     // Length of a box
      double breadth;    // Breadth of a box
      double height;     // Height of a box
}

void main()
{
   Box Box1 = new Box(3.3, 1.2, 1.5);    // Declare box1
   Box Box2 = new Box(8.5, 6.0, 2.0);    // Declare box2

   if(Box1.compare(Box2))
   {
      writeln("Box2 is smaller than Box1");
   }
   else
   {
      writeln("Box2 is equal to or larger than Box1");
   }
}

當上面的程式碼被編譯並執行,它會產生以下結果:

Constructor called.
Constructor called.
Box2 is equal to or larger than Box1