This repository (apple/swift-collections) is a pure Swift library providing high-performance, specialized data structures that extend the Swift standard library. It includes stable modules like DequeModule (ring-buffer deque), OrderedCollections (ordered set/dictionary), HeapModule (min-max heap), BitCollections (BitSet/BitArray), and HashTreeCollections (persistent hash-array mapped trie TreeSet/TreeDictionary). It also contains experimental preview modules (e.g., SortedCollections using B-trees, RopeModule for rope-based BigString, and BasicContainers with non-copyable collections). The code is heavily optimized with copy-on-write, unsafe pointer usage, and advanced Swift ownership features. It is designed for production use with source stability guarantees, while preview modules are explicitly unstable. The library is consumed as a Swift package and integrates seamlessly with standard collection protocols.