Sets

Select a set type

A set holds zero or more members from one ordinal element type. Unlike an array, a set has no ordering, duplicates or numeric indexes.

Type	Element domain	Primary use	Important boundary
TComponentState	Eleven component lifecycle/design flags	Inspect inherited component state	Read-only snapshot controlled by the component framework.
TIdMessageFlagsSet	TIdMessageFlags	IMAP/message state	Local replacement is not an atomic mailbox update.
TLocateOptions	TLocateOption	Dataset Locate matching options	Provider behavior varies and success moves the cursor.
TvxChars	8-bit Char values	Allowed/removed character membership	Cannot represent arbitrary Unicode characters.
TvxSeparators	8-bit Char values	Token separator membership	Each member is an independent one-character separator.

Set syntax and operators

Flags := [mfSeen, mfAnswered];

if mfSeen in Flags then
  Exclude(Flags, mfSeen);

Flags := Flags + [mfFlagged]; // union
Flags := Flags - [mfDeleted]; // difference
Flags := Flags * [mfSeen, mfFlagged]; // intersection

The modified PascalScript compiler/runtime supports:

• [] for the empty set and [A, B] for a set constructor;
• Element in Value for membership;
• Include(Value, Element) and Exclude(Value, Element) for in-place mutation;
• +, - and * for union, difference and intersection;
• =, <>, <= and >= for equality and subset/superset comparisons.

Both operands of a set operation must be the same set type. Set assignment copies the fixed bit field; it does not share backing storage like a dynamic array. Use named members rather than persisting the internal bit pattern, because ordinal changes at the element-type boundary change that representation.

Boundary rules

• A set member's ordinal must fit the type's registered range. The current public types use no more than 256 possible ordinals.
• const set parameters prevent reassignment through that parameter; var parameters and writable properties can replace the caller's complete set.
• Test flags individually when semantics are independent. Equality with a one-member constructor rejects any additional flags.
• An empty set means no selected flags/options; it is not Null and carries no unknown state by itself.
• Character sets are limited to the 8-bit public Char domain even though the current script String is Unicode.

External references

• Embarcadero structured types - Delphi set declarations, constructors and membership.
• Free Pascal set types - compatible ordinal-domain and 256-member limits.
• Free Pascal set operators - compatible membership, mutation and combination operators.

Created 2026-07-15