type 
   TRectangle=class
   private
         FCoordinates:array[0..3] of longint;
         function GetCoordinate(Index:integer):Longint; //讀方法
         procedure SetCoordinate(Index:integer; Value:Longint);//寫方法
    public
          property Left:Lingint;  index 0 read GetCoordinate write SetCoordinate;
          property Top:Lingint;  index 1 read GetCoordinate write SetCoordinate;
          property Right:Lingint;  index 2 read GetCoordinate write SetCoordinate;
          property Bottom:Lingint;  index 3 read GetCoordinate write SetCoordinate;
       end;
 

索引說明2