12.3.1

Changed

• Unsafe chunks have been separated out into the sized-chunks crate, which is now a dependency of im.

12.3.0

Added

• singleton methods have been deprecated and renamed to unit.
• Vector::chunks and Vector::chunks_mut have been deprecated and renamed to leaves and leaves_mut to avoid confusion with Vec::chunks. (#50)

Fixed

• Fixed an issue where the HashMap draining iterator might access uninitialised memory leading to undefined behaviour. (#60)
• Fixed multiple issues in Vector::split_off and Vector::append that would cause lookup errors and unexpectedly unbalanced trees. (#55).

12.2.0

Added

• OrdMap and OrdSet now have a range() method which makes an iterator over a bounded subset of the values. The improved iterator implementation is also considerably more efficient than the previous (about an order of magnitude faster for nontrivial data sets). iter() has been updated to take advantage of this, and is now just an alias for range(..). (#27)
• FocusMut now has an unmut method to turn it into an immutable Focus, releasing its exclusive hold on the underlying Vector.
• Focus now implements Clone.

12.1.0

Added

• Maps and sets now have the clear method just like Vector. (#46)

Changed

• Single chunk Vectors are no longer allocated directly on the stack, meaning that they're now comparable in performance to std::vec::Vec rather than slightly faster, but they also won't eat up your stack space quite as quickly, and they'll clone without copying and share structure with clones as you'd expect.

12.0.0

Starting with this release, the arc flag is gone, in favour of publishing im as two separate crates: im (using Arc) and im-rc (using Rc). They're identical (and built from the same code), except that im is thread safe and im-rc is a little bit more performant.

This is a major release as a consequence, but there should be no breaking code changes other than the new default choice of reference counter.

Added

• The Chunk datatype that's used to build Vector and OrdMap has been exposed and made generally usable. It's somewhere between a GenericArray and a ring buffer, offers O(1)* push in either direction, and is generally hyperoptimised for its purpose of serving as nodes for Bagwell tries, but it's also a powered up version of GenericArray that might be useful to others, hence the public API.
• Vector now has Focus and FocusMut APIs for caching index lookups, yielding huge performance gains when performing multiple adjacent index lookups. Vector::iter has been reimplemented using this API, and is now much simpler and about twice as fast as a result, and Vector::iter_mut now runs nearly an order of magnitude faster. Likewise, Vector::sort and Vector::retain are now using FocusMut and run considerably faster as a result.
• Focus and FocusMut can also be used as stand ins for subslices through the narrow and split_at methods. You can also iterate over foci, making this the most efficient way to iterate over a subset of a Vector.
• Vector now implements Rayon's parallel iterators behind the rayon feature flag.

Changed

• As std::ops::RangeBounds is now stabilised in Rust 1.28, the Vector::slice method is now unconditionally available on the stable channel.
• Union/difference/intersection/is_submap methods on HashMap and OrdMap that take functions now take FnMut instead of Fn. This should not affect any existing code. (#34)
• Vector::split_off can now take an index equal to the length of the vector, yielding an empty vector as the split result. (#33)
• Vector::set now returns the replaced value.

Fixed

• Vector is now represented as a single inline chunk until it grows larger than the chunk size, making it even faster than Vec at small sizes, though clone could now be slower if the clone is expensive (it's still absurdly fast for A: Copy).

11.0.1

Fixed

• Various performance improvements, amounting to a 5-10% speedup for both kinds of map/set.
• Fixed an edge case bug in sort::quicksort.

11.0.0

Changed

This is a major release with many breaking changes, and is intended to stabilise the API more than to denote that the rewrite is now production ready. You should expect future releases with significant performance improvements as well as additional APIs, but there should be no further major release with breaking changes in the immediate future, barring very serious unforeseen issues.

Specifically, you should expect imminent minor releases with performance improvements for Vector and OrdMap, for which I have a number of known optimisations that remain unimplemented.

Thanks to the several contributors without whom im would not be what it is.

No More Arc

All data structures have been reworked to take values of A: Clone instead of Arc<A>, meaning that there's less performance overhead (as well as mental overhead) when using values that clone cheaply. The performance gain when values are A: Copy is a factor of two or more. It's expected that users should wrap values in Arc themselves when using values which are expensive to clone.

Data structures still use reference counters internally to reference nodes, but values are stored directly in the nodes with no further indirection. This is also good for cache locality.

Data structures now use Rc instead of Arc by default to do reference counting. If you need a thread safe version that implements Send and Sync, you can enable the arc feature on the package to compile with Arc instead.

std::collections Compatible API

The API has been reworked to align more closely with std::collections, favouring mutable operations by default, so that operations that were previously suffixed with _mut are now the standard operations, and immutable operations which return a modified copy have been given different names altogether. In short, all your code using previous versions of this library will no longer work, and if it was relying heavily on immutable operations, it's recommended that you rewrite it to be mutable by preference, but you should generally be able to make it work again by using the new method names for the immutable operations.

Here is a list of the most notable changed method names for maps and sets:

Previous immutable	Current immutable	Previous mutable	Current mutable
insert	update	insert_mut	insert
remove	without	remove_mut	remove
pop	extract	pop_mut	remove

You should expect to be able to rewrite code using std::collections::HashMap and std::collections::BTreeMap with minimal or no changes using im::HashMap and im::OrdMap respectively.

Vector has been completely rewritten and has an API that aligns closely with std::collections::VecDeque, with very few immutable equivalents. It's expected that you should use Vector::clone() to take a snapshot when you need it rather than cause an implicit clone for each operation. (It's still O(1) and practically instant.)

I'm considering adding back some of the immutable operations if I can come up with good names for them, but for now, just clone it if you need it.

RRB Vector

Vector is now implemented as an RRB tree with smart head/tail chunking, obsoleting the previous Hickey trie implementation.

RRB trees have generally similar performance characteristics to the Hickey trie, with the added benefit of having O(log n) splitting and concatenation.

Operation	RRB tree	Hickey trie	Vec	VecDeque
Push front	O(1)*	O(log n)	O(n)	O(1)*
Push back	O(1)*	O(log n)	O(1)*	O(1)*
Pop front	O(1)*	O(log n)	O(n)	O(1)*
Pop back	O(1)*	O(log n)	O(1)	O(1)*
Lookup by index	O(log n)	O(log n)	O(1)	O(1)
Split	O(log n)	O(log n)	O(n)	O(n)
Join	O(log n)	O(n)	O(n)	O(n)

(Please note that the timings above are for the im version of the Hickey trie, based on the Immutable.js implementation, which performs better than the original Clojure version on splits and push/pop front, but worse on push/pop back).

The RRB tree is the most generally efficient list like data structure currently known, to my knowledge, but obviously it does not and cannot perform as well as a simple Vec on certain operations. It makes up for that by having no operations you need to worry about the performance complexity of: nothing you can do to an RRB tree is going to be more expensive than just iterating over it. For larger data sets, being able to concatenate (and, by extension, insert and remove at arbitrary locations) several orders of magnitude faster than Vec could also be considered a selling point.

No More CatList And ConsList

CatList has been superseded by Vector, and ConsList was generally not very useful except in the more peculiar edge cases where memory consumption matters more than performance, and keeping it in line with current API changes wasn't practical.

No More Funny Words

Though it breaks my heart, words like cons, snoc, car, cdr and uncons are no longer used in the im API, to facilitiate closer alignment with std::collections. Even the head/tail pair is gone, though head and last remain as aliases for front and back.

10.2.0

[10.2.0] - 2018-04-15

Added

• Map/set methods which accept references to keys will now also take
  any value that's borrowable to the key's type, ie. it will take a
  reference to a type Borrowable where the key implements
  Borrow<Borrowable>. This is particularly handy for types such as
  String because you can now pass &str to key lookups instead of
  &String. So, instead of the incredibly cumbersome
  map.get(&"foo".to_string()) you can just do map.get("foo") when
  looking up a mapping for a string literal.

10.1.0

[10.1.0] - 2018-04-12

Added

• Vector, OrdMap and HashMap now implement Index and
  IndexMut, allowing for syntax like map[key] = value.
• Added cons, snoc, uncons and unsnoc aliases where they were missing.
• Everything now implements Sum and Extend where possible.

Changed

• Generalised OrdMap/OrdSet's internal nodes so OrdSet now only
  needs to store pointers to its values, not pairs of pointers to
  value and Unit. This has caused OrdMap/Set's type constraints to
  tighten somewhat - in particular, iteration over maps/sets whose
  keys don't implement Ord is no longer possible, but as you would
  only have been able to create empty instances of these, no sensible
  code should break because of this.
• HashMap/HashSet now also cannot be iterated over unless they
  implement Hash + Eq, with the same note as above.
• Constraints on single operations that take closures on HashMap and
  OrdMap have been relaxed from Fn to FnOnce. (Fixes #7.)

Fixed

• Hashes are now stored in HashMaps along with their associated
  values, removing the need to recompute the hash when a value is
  reordered inside the tree.

[10.0.0] - 2018-03-25

This is the first release to be considered reasonably stable.

Available data structures:

• HashSet/HashMap: unordered maps based on hash array mapped tries.
• OrdSet/OrdMap: ordered maps based on B-trees.
• Vector: indexable double ended queues.
• CatList: double ended queues with instant concatenation.
• ConsList: the classic.