Object: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: Object

New		Line
1	+	Back to: [[Data type\|data types]] \\| [[Reserved words\|reserved words]].
2	+
3	+	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\|class]] in the types it can create, but by default objects are created on the [[Stack\|stack]], while class data is created on the [[Heap\|heap]]. However, object created types can be created on the heap by using the [[New\|new]] procedure. Object was introduced in [[Turbo Pascal]], while [[Class\|class]] was introduced in [[Delphi]]. Object is maintained for backward compatibility with Turbo Pascal and has largely been superseded by [[Class\|class]].
4	+
5	+	Example skeleton of the creation of the data type object:
6	+
7	+	``` pascal
8	+	type
9	+	TTest = object
10	+	private
11	+	{ private declarations }
12	+	public
13	+	{ public declarations }
14	+	end;
15	+	```
16	+
17	+	Example skeleton of the create of a packed version of the data type object:
18	+
19	+	``` pascal
20	+	type
21	+	TTest = packed object
22	+	private
23	+	{ private declarations }
24	+	public
25	+	{ public declarations }
26	+	end;
27	+	```
28	+
29	+	Example with constructor and destructor:
30	+
31	+	``` pascal
32	+	type
33	+	TTest = object
34	+	private
35	+	{private declarations}
36	+	total_errors : Integer;
37	+	public
38	+	{public declarations}
39	+	constructor Init;
40	+	destructor Done;
41	+	procedure IncrementErrors;
42	+	function GetTotalErrors : Integer;
43	+	end;
44	+
45	+	procedure TTest.IncrementErrors;
46	+	begin
47	+	Inc(total_errors);
48	+	end;
49	+
50	+	function TTest.GetTotalErrors : Integer;
51	+	begin
52	+	GetTotalErrors := total_errors;
53	+	end;
54	+
55	+	constructor TTest.Init;
56	+	begin
57	+	total_errors := 0;
58	+	end;
59	+
60	+	destructor TTest.Done;
61	+	begin
62	+	WriteLn('Destructor not needed - nothing allocated on the heap');
63	+	end;
64	+
65	+	var
66	+	error_counter: TTest;
67	+
68	+	begin
69	+	error_counter.Init; // unlike C++, constructors must be explicitly called
70	+	error_counter.IncrementErrors;
71	+	error_counter.IncrementErrors;
72	+	WriteLn('current errors:', error_counter.GetTotalErrors);
73	+	error_counter.Done
74	+	end.
75	+	```
76	+
77	+	Output:\
78	+	current errors:2\
79	+	Destructor not needed - nothing allocated on the heap
80	+
81	+	## Objects compared to other structured types
82	+
83	+	## See Also
84	+
85	+	- [[Programming Using Objects]]
86	+
87	+	---
88	+	From the Free Pascal wiki, page "Object", as it stood on 2021-02-17 after a change by Jwdietrich, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

Back to history