Sets

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A set is a collection of ordinal values of the same type. If you are coming to Delphi Prism via C#, the concept of sets may be new to you. Sets are a convenient way of storing and accessing values that belong together.

For example, instead of defining day, month and year as 1, 2 and 3, it is more convenient to declare them as a set.

Although you can fill sets with integers, you will typically use them to hold Enums:

Type
  MySet1 = set of 1000; // set with elements 0..999
  MySet2 = set of (Abc, Def, Ghi);  // implicit enums

You can also declare a set using an explicit enum:

type
  MyEnum = (Abc, Def, Ghi);
  MySet3 = Set of MyEnum; // creates a copy of all possible values in the enum;

A set is a value type and typical syntax is as follows:

var x: MySet3 := [MySet.Def, MySet.Abc]; // note MySet, not MyEnum

Additional Syntax

set of byte // same as set of 256
set of 256 // same as set of 0..255
set of Word // same as set of 65536
set of 65536 // same as set of 0..65535

Set Operators

The following operators take two sets as operands and return a third set:

Operator	Operation	Example
+	union	[a,b,e]+[c,e,f] = [a,b,c,e,f]
-	difference	[a,b,c,d]-[a,c] = [b,d]
*	intersection	[a,b,e]*[c,e,f] = [e]

These operators compare two sets:

Operator	Operation	Example
=	equality	[a,b,c] = [a,b,c] // true [a,b,c] = [a,b,c,d] // false [a,b,e] = [a,b,d] // false [a,b,c,d] = [a,b,c] // false
<>	inequality	[a,b,c] <> [a,b,c] // false [a,b,c] <> [a,b,c,d] // true [a,b,e] <> [a,b,d] // true [a,b,c,d] <> [a,b,c] // true
<=	subset	[a,b,c] <= [a,b,c] // true [a,b,c] <= [a,b,c,d] // true [a,b,e] <= [a,b,d] // false [a,b,c,d] <= [a,b,c] // false
>=	superset	[a,b,c] >= [a,b,c] // true [a,b,c] >= [a,b,c,d] // false [a,b,e] >= [a,b,d] // false [a,b,c,d] >= [a,b,c] // true

Finally, the in operator lets you test set membership:

Operator	Operation	Example
in	membership	if a in [a,b,c] then .. // True if x not in foo then... // shortcut for if not (x in foo) then

Set Rules

• Elements of the set cannot have a value < 0 (this is why signed datatypes are not supported).

• The set uses 1 bit possible values, 8 bits per byte.

• The maximum number of set values is limited to the available memory required to store that bit-set.

• The generic class used for sets is immutable, set1 + set2 returns a new set.

• A set with nothing does not occupy memory for all possible bit values, only the highest bit that is set will define how much byte memory will be allocated.

• The supported set sub-types are: byte, word, char and enumerated types.

External use of Sets

Sets may be used from non-Delphi Prism code, including all operators except 'in'.

In needs to be called via the op_in method or via the regular methods on the set class in C#.

See Also

• Types

Area: Oxygene Language
Compiler version: Oxygene 5

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