Delphi in a Nutshell

Name

Is Keyword

Syntax

Object reference is Class reference

Description

The is operator tests whether the type of an object reference is the same as a given class reference or is a descendant of that class. It returns True if the object has the same type or is derived from the class type; it returns False otherwise.

Tips and Tricks

• To test the type of an interface, call QueryInterface or the Supports function in the SysUtils unit.

• The is operator calls the object’s InheritsFrom method.

• If you have tested an object’s type with the is operator, you do not need to use the as operator. Use a plain type cast for better performance.

• The is operator requires an object reference as the left-hand operand. To test a class reference, call the InheritsFrom method of TObject.

Example

// Double-click any edit box to clear it. Set the OnDblClick handler
// for all edit boxes to this procedure.
procedure TForm1.EditDblClick(Sender: TObject);
begin
  if Sender is TCustomEdit then
    TCustomEdit(Sender).Clear;
end;

See Also

As Keyword, Class Type, TObject Type