identifierset

An identifierset is a data structure or collection that stores a set of distinct identifiers. An identifier may be a string, an integer, a UUID, or any value used to uniquely reference an entity such as a user, resource, or record. The defining property is that each identifier occurs at most once within the collection, regardless of insertion order.

Identifiersets support basic set operations and membership queries. Common operations include add, remove, and contains, as well as size and emptiness checks. Many implementations also provide set-theoretic operations such as union, intersection, and difference, enabling efficient combination and comparison of identifier collections.

Common implementations include hash-based sets for fast average-case lookups, and tree-based sets for ordered iteration. Some languages offer immutable or persistent variants that share structure between versions. In performance-sensitive contexts, a bitset may be used when the range of possible identifiers is dense and small.

Applications include de-duplicating identifiers in data processing, tracking active sessions or devices, quickly verifying membership in access control lists, and indexing resources for fast lookup. Identifiersets are also used in graph algorithms and database query planning to represent groups of entity keys.

Design considerations include the type and normalization of identifiers, handling of case sensitivity, memory usage, and concurrency in multi-threaded environments. When identifiers come from external sources, validation and canonicalization help maintain a consistent set.

See also Set, Hash set, Tree set, Bitset, Persistent data structure.