Principally defines indexed class data properties
1.Property Name : Property-type Index Constant Read Getter Write Setter;
 2.Property Name[Index : Index type] : Property-type Read Getter Write Setter;
 3.Function|Procedure Index Constant;
 4.Function|Procedure header; External DllName Index Constant;
The Index directive is principally used to declare indexed class data properties.
These principally work against array or list types of data.
Version 1
Retrieves or writes an indexed value by specifying a Constant index number.
Version 2
Retrieves or writes an indexed value by specifying an index parameter. As can be seen, this does not actually use the Index directive - it is included here for completeness.
See the example or the Property keyword for information about coding the routines associated with these properties.
Version 3
Defines a unique index for routine when exporting.
Version 4
Defines the unique index of an external routine being imported.
Related commands
FunctionDefines a subroutine that returns a value
ProcedureDefines a subroutine that does not return a value
PropertyDefines controlled access to class fields
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Example code : Illustrate both varieties of Indexed properties
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.

unit Unit1;


  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  // Class with Indexed properties
  TRectangle = class
    fCoords: array[0..3] of Longint;
    function  GetCoord(Index: Integer): Longint;
    procedure SetCoord(Index: Integer; Value: Longint);
    property Left   : Longint Index 0 read GetCoord write SetCoord;
    property Top    : Longint Index 1 read GetCoord write SetCoord;

    property Right  : Longint Index 2 read GetCoord write SetCoord;
    property Bottom : Longint Index 3 read GetCoord write SetCoord;
    property Coords[Index: Integer] : Longint read GetCoord write SetCoord;

  // The form class itself
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);

  Form1: TForm1;


{$R *.dfm}

// TRectangle property 'Getter' routine
function TRectangle.GetCoord(Index: Integer): Longint;
  // Only allow valid index values
  if (Index >= 0) and (Index <= 3)
  then Result := fCoords[Index]
  else Result := -1;

// TRectangle property 'Setter' routine
procedure TRectangle.SetCoord(Index, Value: Integer);
  // Only allow valid index values
  if (Index >= 0) and (Index <= 3)
  then fCoords[Index] := Value;

// Main line code
procedure TForm1.FormCreate(Sender: TObject);
  myRect : TRectangle;
  i : Integer;

  // Create my little rectangle
  myRect := TRectangle.Create;

  // And set the corner coordinates
  myRect.Left := 22;      // Left using direct method
  myRect.Top  := 33;
  myRect.SetCoord(2,44);  // Right using indexed method

  // And ask for these values
  for i:= 0 to 3 do
    ShowMessage('myRect coord '+IntToStr(i)+' = '+intToStr(myRect.GetCoord(i)));

  myRect coord 0 = 22
  myRect coord 1 = 33
  myRect coord 2 = 44
  myRect coord 3 = 55
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