Record: what changed

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Title: Record

New		Line
1	+	A `record` is a highly structured data [[Type\|type]] in [[Pascal]]. They are widely used in Pascal, to group data items together logically.
2	+
3	+	While simple data structures such as [[Array\|arrays]] or sets consist of elements all of the same type, a record can consist of a number of elements of different types, and can take on a huge complexity. Each separate part of a record is referred to as a field.
4	+
5	+	The word `record` is a [[Reserved word\|reserved word]].
6	+
7	+	## Declaration
8	+
9	+	### Fixed structure
10	+
11	+	``` pascal
12	+	type
13	+	TMember = record
14	+	firstname, surname : string;
15	+	address: array [1..3] of string;
16	+	phone: string;
17	+	birthdate: TDateTime;
18	+	paidCurrentSubscription: boolean
19	+	end;
20	+	```
21	+
22	+	### Variable structure
23	+
24	+	And even more complex structures are possible, e.g.:
25	+
26	+	``` pascal
27	+	type
28	+	TMaritalState = (unmarried, married, widowed, divorced);
29	+	TPerson = record
30	+	// CONSTANT PART
31	+	// of course records may be nested
32	+	name: record
33	+	first, middle, last: string;
34	+	end;
35	+	sex: (male, female);
36	+	// date of birth
37	+	dob: TDateTime;
38	+	// VARIABLE PART
39	+	case maritalState: TMaritalState of
40	+	unmarried: ( );
41	+	married, widowed: (marriageDate: TDateTime);
42	+	divorced: (marriageDateDivorced, divorceDate: TDateTime;
43	+	isFirstDivorce: boolean)
44	+	end;
45	+	```
46	+
47	+	Note that fields of the variable part have to be in parentheses. You cannot use the same identifier multiple times, so a slightly different name has to be used for the `marriageDate` in case of divorced.
48	+
49	+	The variable part shares the same memory. So `marriageDate` and `marriageDateDivorced` will have the same value regardless of `maritalState`. This behaviour is particularly practical as the following example shows:
50	+
51	+	``` pascal
52	+	type
53	+	TSpecialWord = record
54	+	case Byte of
55	+	0: (Word_value: Word); // 7
56	+	1: (Byte_low, Byte_high: Byte); // 7, 0
57	+	2: (Bits: bitpacked array [0..15] of 0..1); // 1, 1, 1, 0, 0, ...
58	+	end;
59	+	```
60	+
61	+	This record has only a variable part and enables access to the value of the word, the individual bytes and even to the bits. An identifier is not necessarily required in the `case` clause, so this does not occupy any memory. The size of this record is two bytes. In the case of `Bits`, this is only possible if `bitpacked` is used. Note the order of the bytes, with the less significant byte (LSB) coming first.
62	+
63	+	### Advanced record
64	+
65	+	An “advanced record” is a record with [[Method\|methods]], [[Property\|properties]] and [[management operators]]
66	+
67	+	> Note: Remember to add a compiler directive `{$modeSwitch advancedRecords}` (after you have set the mode).
68	+
69	+	## Addressing
70	+
71	+	### Fields
72	+
73	+	Individual fields are accessed by placing a dot between the record name and the field name thus:
74	+
75	+	``` pascal
76	+	a.firstname := 'George';
77	+	a.surname := 'Petersen';
78	+	a.phone := '789534';
79	+	a.paidCurrentSubscription := true;
80	+	```
81	+
82	+	Alternatively, the whole series of fields can be made available together using the [[With\|with-construct]]:
83	+
84	+	``` pascal
85	+	with a do
86	+	begin
87	+	firstname := 'George';
88	+	surname := 'Petersen';
89	+	phone := '789534';
90	+	paidCurrentSubscription := true
91	+	end;
92	+	```
93	+
94	+	### Instances
95	+
96	+	A record is treated by the program as a single entity, and for example a whole record can be copied (provided the copy is of the same type) thus:
97	+
98	+	``` pascal
99	+	var
100	+	a, b: TMember;
101	+
102	+	(* main program *)
103	+	begin
104	+	// ... assign values to the fields in record a
105	+	b := a
106	+	// Now b holds a _copy_ of a.
107	+	// Do not get confused with references:
108	+	// a and b still point to _different_ _entities_ of TMember.
109	+	end.
110	+	```
111	+
112	+	## Constant record
113	+
114	+	``` pascal
115	+	type
116	+	// record definition
117	+	TSpecialDay = record
118	+	dayName: string;
119	+	month: integer;
120	+	day: integer;
121	+	end;
122	+
123	+	const
124	+	// TSpecialDay constant
125	+	christmasDay: TSpecialDay = (
126	+	dayName: 'Christmas Day';
127	+	month: 12;
128	+	day: 25;
129	+	);
130	+
131	+	// since FPC 3.2.0 you may define an constant array of records like this
132	+	const
133	+	SpecialDays: array of TSpecialDay = (
134	+	( dayName: 'Christmas Day' ; month: 12; day: 25),
135	+	( dayName: 'New Year''s Day'; month: 1; day: 1)
136	+	);
137	+	```
138	+
139	+	## Records compared to other structured types
140	+
141	+	## See also
142	+
143	+	- [[Basic Pascal Tutorial/Chapter 5/Records\|Records]], tutorial that covers records
144	+	- [[Object\|object]]
145	+	- [[Class\|class]]
146	+
147	+	---
148	+	From the Free Pascal wiki, page "Record", as it stood on 2022-11-28 after a change by Dbannon, 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).
149	+	Category: Code

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