Set: what changed

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Title: Set

New		Line
1	+	Back to [[Data type\|data types]].
2	+
3	+	Back to [[Reserved words]].
4	+
5	+	## Introduction
6	+
7	+	A Set encodes many values from an enumeration into an Ordinal type.
8	+
9	+	For example let's consider this enumeration:
10	+
11	+	``` pascal
12	+	TSpeed = (spVerySlow,spSlow,spAverage,spFast,spVeryFast);
13	+	```
14	+
15	+	And this set:
16	+
17	+	``` pascal
18	+	TPossibleSpeeds = set of TSpeed
19	+	```
20	+
21	+	[[Constant]] instances of TPossibleSpeeds can be defined using [[square brackets\|brackets]] to hold set elements:
22	+
23	+	``` pascal
24	+	const
25	+	RatherSlow = [spVerySlow,spSlow];
26	+	RatherFast = [spFast,spVeryFast];
27	+	```
28	+
29	+	RatherSlow and RatherFast are some Set of TSpeed.
30	+
31	+	## Manipulating sets
32	+
33	+	You can assign a set's contents directly:
34	+
35	+	``` pascal
36	+	var
37	+	SomeSpeeds: TPossibleSpeeds = [spAverage];
38	+	begin
39	+	SomeSpeeds := [spSlow,spVerySlow];
40	+	end;
41	+	```
42	+
43	+	Two [[Function\|functions]] defined in the [[RTL]] [[System unit]] are used to manipulate set elements individually: [[Include]](ASet,AValue) and [[Exclude]](ASet,AValue).
44	+
45	+	``` pascal
46	+	var
47	+	SomeSpeeds: TPossibleSpeeds;
48	+	begin
49	+	SomeSpeeds := [];
50	+	Include(SomeSpeeds,spVerySlow);
51	+	Include(SomeSpeeds,spVeryFast);
52	+	end;
53	+	```
54	+
55	+	Sets cannot be directly manipulated if they are published. You usually have to make a local copy, change the local copy and then to call the setter.
56	+
57	+	``` pascal
58	+	procedure TSomething.DoSomething(Sender: TFarObject);
59	+	var
60	+	LocalCopy: TPossibleSpeeds;
61	+	begin
62	+	LocalCopy := Sender.PossibleSpeeds; // getter to local
63	+	Include(LocalCopy,spVerySlow);
64	+	Sender.PossibleSpeeds := LocalCopy; // local to setter.
65	+	end;
66	+	```
67	+
68	+	The [[Reserved word\|reserved word]] [[In\|in]] is also used to test if a value is in a set. It's usually used in this fashion:
69	+
70	+	``` pascal
71	+	var
72	+	CanBeSlow: Boolean;
73	+	const
74	+	SomeSpeeds = [Low(TSpeed)..High(TSpeed)];
75	+	begin
76	+	CanBeSlow := (spVerySlow in SomeSpeeds) or (spSlow in SomeSpeeds);
77	+	end;
78	+	```
79	+
80	+	Empty square brackets represent an empty set. You can test if a set currently contains no values at all by comparing against an empty set:
81	+
82	+	``` pascal
83	+	var
84	+	SomeSpeeds: TPossibleSpeeds;
85	+	begin
86	+	if SomeSpeeds = [] then SomeSpeeds := [spAverage];
87	+	end;
88	+	```
89	+
90	+	## Bitmasks
91	+
92	+	Sets can be used to create bitmasks as shown in the example.
93	+
94	+	``` pascal
95	+	(*
96	+	The set [FLAG_A, FLAG_C] will be stored like this:
97	+
98	+	TFlags : 0000'0101
99	+	│││
100	+	FLAG_C ──────────┘││
101	+	FLAG_B ───────────┘│
102	+	FLAG_A ────────────┘
103	+	*)
104	+
105	+	type
106	+	TFlag = (FLAG_A, FLAG_B, FLAG_C);
107	+	TFlags = set of TFlag;
108	+
109	+	var
110	+	Flags: TFlags;
111	+
112	+	[..]
113	+	Flags:= [FLAG_A, FLAG_C];
114	+	if FLAG_A in Flags then .. // check FLAG_A is set in flags variable
115	+	```
116	+
117	+	---
118	+	From the Free Pascal wiki, page "Set", as it stood on 2022-07-16 after a change by Kirinn, 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).

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