Objectset

An objectset is a programming construct that stores a collection of unique objects. It supports standard set operations such as add, remove, contains, and size, as well as set-theoretic operations like union, intersection, and difference. In an objectset, elements are maintained without duplicates and can be iterated in some defined order depending on implementation.

Semantics: element identity versus equality. Some languages define equality by a set of fields (structural equality), while others use object identity (reference). In identity-based objectsets, two separate objects with identical content are distinct elements; in value-based sets, they may be treated as equal if their values compare equal. The precise rules depend on the language and the chosen representation.

Implementation and performance: most objectsets rely on a hash table to achieve fast membership tests and insertions, with average-case constant time for add, contains, and remove, and linear time in the size of the set for certain operations. Ordered variants may preserve insertion order or sort elements, which can affect performance characteristics. Some languages provide weak-object sets that hold weak references to elements, allowing garbage collection when no strong references exist elsewhere.

Examples and use cases: objectsets are useful for deduplicating items, performing fast membership tests, caching keys, and tracking visited nodes in graph traversals. They are a common building block in algorithms that require a collection of distinct items and efficient existence checks, and they often interact with language-specific rules for hashing, equality, and garbage collection.

See also: set, hash table, weak set, identity, equality.