lenobjdict

Lenobjdict is a term used to describe a dictionary‑like data structure that uses the length of its keys as a secondary index to enable fast length-based queries. It is not a standard library type, but a conceptual or user‑defined extension of a regular map that adds an auxiliary index alongside the primary key–value store.

In a typical lenobjdict design, there is a primary mapping from keys to values, similar to a standard dictionary, and an auxiliary index that records the lengths of keys. This enables operations such as retrieving all entries where the key has a specific length, or grouping entries by key length. The primary map handles exact key lookups, while the length index supports range and filter queries based on key length.

Semantics and implementation considerations vary. Keys are still hashed according to the language’s rules, but the structure must ensure the length index stays consistent when keys are inserted, updated, or removed. Some implementations may use weak references for keys to avoid preventing garbage collection, trading off simplicity for memory efficiency. Performance characteristics depend on workload; the extra index improves length-based queries at the cost of additional memory and maintenance logic.

Common use cases involve datasets where key length correlates with processing cost or categorization needs, such as text processing, token analysis, or identifier management. Variants may include distinguishing by length of the key’s string representation or extending the concept to multi-dimensional indices (length, hash, or other key-derived metrics).

See also: dictionary, weak-key dictionary, indexing structures.