Unordered polymorphic collections have been added to Boost.PolyCollection, employing boost::container::hub‑based segments to achieve iterator and reference stability. In contrast to the existing ordered variants, these collections use a different internal structure that yields insertion speeds comparable to or faster than their ordered counterparts, while iteration performance is slower due to the lack of vector‑based traversal. The new unordered collections (base, function, any, and variant) are scheduled for inclusion in Boost 1.93. Internally, all eight collection types are instantiated from a common poly_collection template parameterized by a model that specifies the polymorphism technique, ordering, and openness, creating a flexible three‑dimensional design. An article titled “Inside Boost.PolyCollection” documents this architecture in detail.
