Object

│ Deutsch (de) │ English (en) │ français (fr) │
Back to: data types | reserved words.

The reserved word object is used to construct complex data types that contain both functions, procedures and data. Object allows the user to perform Object-Oriented Programming (OOP). It is similar to class in the types it can create, but by default objects are created on the stack, while class data is created on the heap. However, object created types can be created on the heap by using the new procedure. Object was introduced in Turbo Pascal, while class was introduced in Delphi. Object is maintained for backward compatibility with Turbo Pascal and has largely been superseded by class.

Example skeleton of the creation of the data type object:

type
  TTest = object
  private
    { private declarations }
  public
    { public declarations }
  end;

Example skeleton of the create of a packed version of the data type object:

type
  TTest = packed object
  private
    { private declarations }
  public
    { public declarations }
  end;

Example with constructor and destructor:

type
   TTest = object
   private 
     {private declarations}
     total_errors : Integer;
   public
     {public declarations}
     constructor Init;
     destructor Done;
     procedure IncrementErrors;
     function GetTotalErrors : Integer;
   end;

procedure TTest.IncrementErrors;
begin
  Inc(total_errors);
end;
    
function TTest.GetTotalErrors : Integer;
begin
   GetTotalErrors := total_errors;
end;

constructor TTest.Init;
begin
  total_errors := 0;
end;

destructor TTest.Done;
begin
   WriteLn('Destructor not needed - nothing allocated on the heap');
end;

var
   error_counter: TTest;

begin
   error_counter.Init; // unlike C++, constructors must be explicitly called
   error_counter.IncrementErrors;
   error_counter.IncrementErrors;
   WriteLn('current errors:', error_counter.GetTotalErrors);
   error_counter.Done
end.

Output:
current errors:2
Destructor not needed - nothing allocated on the heap

Objects compared to other structured types

Feature	Record	Adv Record	Object	Class
Encapsulation (combining data and methods + hiding visibility)	No	Yes	Yes	Yes
Inheritance	No	No	Yes	Yes
Class constructor and destructor	No	Yes	Yes	Yes
Polymorphism (virtual methods)	No	No	Yes	Yes
Memory allocation	Stack	Stack	Stack	Heap (Only)
Setting fields to zero on allocation	Managed Types only	Managed Types only	Managed Types only	All fields
Default() function returns a constant with	all fields zeros	all fields zeros	all fields zeros	returns nil
Operator overload (global)	Yes	Yes	Yes	Yes
Operator overload (in type only)	No	Yes	No	No
Type helpers	No	Yes	No	Yes
Virtual constructors, class reference	No	No	No	Yes
Variant part (case) as c/c++ union	Yes	Yes	No	No
Bitpacked (really packing)	Yes	Yes	No	No

Modified from https://forum.lazarus.freepascal.org/index.php/topic,30686.30.html (original author: ASerge).

See Also

• Programming Using Objects