Tests whether an object is a certain class or ascendant
  Object reference Is Class reference
The Is keyword is used to test to see whether an object belongs to a class, or parent of that class.
For example, you may test to see whether a graphical component (normally called 'Sender') is a TButton, or TList or whatever.
All objects belong to the TObject class, from which they are ultimately derived.
Related commands
As Used for casting object references
Class Starts the declaration of a type of object class
Object Allows a subroutine data type to refer to an object method
TObject The base class type that is ancestor to all other classes
 Author links

 Buy Website Traffic at

 Buy Proxies at
 Download this web site as a Windows program.

Example code : Illustrate use of is on a class hierarchy
// 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;


  Forms, Dialogs, Classes, Controls, StdCtrls;

  // Define new class types
  TFruit = class
    name : string;
    constructor Create(name : string);
  // Define two descendant types
  TApple = class(TFruit);
  TPear  = class(TFruit);
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);

  Form1: TForm1;

{$R *.dfm} // Include form definitions

// Create a fruit object
constructor TFruit.Create(name: string);
begin := name;

procedure TForm1.FormCreate(Sender: TObject);
  fruit  : TFruit;
  apple  : TApple;
  pear   : TPear;
  // Create 2 different fruit objects
  apple  := TApple.Create('Pink Lady');
  pear   := TPear.Create('Comice');

  // They are both TFruit or descendant types
  if apple  Is TFruit then ShowMessage( +' is a fruit');
  if pear   Is TFruit then ShowMessage(  +' is a fruit');

  // Apple is also a TApple type
  fruit := apple;
  if fruit Is TApple then ShowMessage(  +' is an apple');

  // But apple is not a pear
  if fruit Is TPear    // 'if apple is TPear' does not compile
  then ShowMessage(' is a pear')
  else ShowMessage(' is not a pear');
   Pink lady is a fruit
   Comice is a fruit
   Pink lady is an apple
   Pink lady is not a pear
Delphi Programming Neil Moffatt 2002 - 2016. All rights reserved.  |  Home Page