[#changes]
= Change Log

:idprefix: changes_
:svn-ticket-url: https://svn.boost.org/trac/boost/ticket
:github-pr-url: https://github.com/boostorg/unordered/pull
:cpp: C++

== Release 1.86.0

* Added container `pmr` aliases when header `<memory_resource>` is available. The alias `boost::unordered::pmr::[container]` refers to `boost::unordered::[container]` with a `std::pmr::polymorphic_allocator` allocator type.
* Equipped open-addressing and concurrent containers to internally calculate and provide statistical metrics affected by the quality of the hash function. This functionality is enabled by the global macro `BOOST_UNORDERED_ENABLE_STATS`.
* Avalanching hash functions must now be marked via an `is_avalanching` typedef with an embedded `value` constant set to `true` (typically, defining `is_avalanching` as `std::true_type`). `using is_avalanching = void` is deprecated but allowed for backwards compatibility.
* Added Visual Studio Natvis framework custom visualizations for containers and iterators. This works for all containers with an allocator using raw pointers. In this release, containers and iterators are not supported if their allocator uses fancy pointers. This may be addressed in later releases.

== Release 1.85.0

* Optimized `emplace()` for a `value_type` or `init_type` (if applicable) argument to bypass creating an intermediate object. The argument is already the same type as the would-be intermediate object.
* Optimized `emplace()` for `k,v` arguments on map containers to delay constructing the object until it is certain that an element should be inserted. This optimization happens when the map's `key_type` is move constructible or when the `k` argument is a `key_type`.
* Fixed support for allocators with `explicit` copy constructors ({github-pr-url}/234[PR#234^]).
* Fixed bug in the `const` version of `unordered_multimap::find(k, hash, eq)` ({github-pr-url}/238[PR#238^]).

== Release 1.84.0 - Major update

* Added `boost::concurrent_flat_set`.
* Added `[c]visit_while` operations to concurrent containers,
with serial and parallel variants.
* Added efficient move construction of `boost::unordered_flat_(map|set)` from
`boost::concurrent_flat_(map|set)` and vice versa.
* Added bulk visitation to concurrent containers for increased lookup performance.
* Added debug-mode mechanisms for detecting illegal reentrancies into
a concurrent container from user code.
* Added Boost.Serialization support to all containers and their (non-local) iterator types.
* Added support for fancy pointers to open-addressing and concurrent containers.
  This enables scenarios like the use of Boost.Interprocess allocators to construct containers in shared memory.
* Fixed bug in member of pointer operator for local iterators of closed-addressing
  containers ({github-pr-url}/221[PR#221^], credit goes to GitHub user vslashg for finding
  and fixing this issue).
* Starting with this release, `boost::unordered_[multi]set` and `boost::unordered_[multi]map`
  only work with C++11 onwards.

== Release 1.83.0 - Major update

* Added `boost::concurrent_flat_map`, a fast, thread-safe hashmap based on open addressing.
* Sped up iteration of open-addressing containers.
* In open-addressing containers, `erase(iterator)`, which previously returned nothing, now
returns a proxy object convertible to an iterator to the next element.
This enables the typical `it = c.erase(it)` idiom without incurring any performance penalty
when the returned proxy is not used.

== Release 1.82.0 - Major update

* {cpp}03 support is planned for deprecation. Boost 1.84.0 will no longer support
  {cpp}03 mode and {cpp}11 will become the new minimum for using the library.
* Added node-based, open-addressing containers
  `boost::unordered_node_map` and `boost::unordered_node_set`.
* Extended heterogeneous lookup to more member functions as specified in
  https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2363r5.html[P2363].
* Replaced the previous post-mixing process for open-addressing containers with
  a new algorithm based on extended multiplication by a constant.
* Fixed bug in internal emplace() impl where stack-local types were not properly
  constructed using the Allocator of the container which breaks uses-allocator
  construction.

== Release 1.81.0 - Major update

* Added fast containers `boost::unordered_flat_map` and `boost::unordered_flat_set`
  based on open addressing.
* Added CTAD deduction guides for all containers.
* Added missing constructors as specified in https://cplusplus.github.io/LWG/issue2713[LWG issue 2713].

== Release 1.80.0 - Major update

* Refactor internal implementation to be dramatically faster
* Allow `final` Hasher and KeyEqual objects
* Update documentation, adding benchmark graphs and notes on the new internal
  data structures

== Release 1.79.0

* Improved {cpp}20 support:
  ** All containers have been updated to support
    heterogeneous `count`, `equal_range` and `find`.
  ** All containers now implement the member function `contains`.
  ** `erase_if` has been implemented for all containers.
* Improved {cpp}23 support:
  ** All containers have been updated to support
    heterogeneous `erase` and `extract`.
* Changed behavior of `reserve` to eagerly
  allocate ({github-pr-url}/59[PR#59^]).
* Various warning fixes in the test suite.
* Update code to internally use `boost::allocator_traits`.
* Switch to Fibonacci hashing.
* Update documentation to be written in AsciiDoc instead of QuickBook.

== Release 1.67.0

* Improved {cpp}17 support:
  ** Add template deduction guides from the standard.
  ** Use a simple implementation of `optional` in node handles, so
    that they're closer to the standard.
  ** Add missing `noexcept` specifications to `swap`, `operator=`
    and node handles, and change the implementation to match.
    Using `std::allocator_traits::is_always_equal`, or our own
    implementation when not available, and
    `boost::is_nothrow_swappable` in the implementation.
* Improved {cpp}20 support:
  ** Use `boost::to_address`, which has the proposed {cpp}20 semantics,
    rather than the old custom implementation.
* Add `element_type` to iterators, so that `std::pointer_traits`
  will work.
* Use `std::piecewise_construct` on recent versions of Visual {cpp},
  and other uses of the Dinkumware standard library,
  now using Boost.Predef to check compiler and library versions.
* Use `std::iterator_traits` rather than the boost iterator traits
  in order to remove dependency on Boost.Iterator.
* Remove iterators' inheritance from `std::iterator`, which is
  deprecated in {cpp}17, thanks to Daniela Engert
  ({github-pr-url}/7[PR#7^]).
* Stop using `BOOST_DEDUCED_TYPENAME`.
* Update some Boost include paths.
* Rename some internal methods, and variables.
* Various testing improvements.
* Miscellaneous internal changes.

== Release 1.66.0

* Simpler move construction implementation.
* Documentation fixes ({github-pr-url}/6[GitHub #6^]).

== Release 1.65.0

* Add deprecated attributes to `quick_erase` and `erase_return_void`.
  I really will remove them in a future version this time.
* Small standards compliance fixes:
  ** `noexpect` specs for `swap` free functions.
  ** Add missing `insert(P&&)` methods.

== Release 1.64.0

* Initial support for new {cpp}17 member functions:
  `insert_or_assign` and `try_emplace` in `unordered_map`,
* Initial support for `merge` and `extract`.
  Does not include transferring nodes between
  `unordered_map` and `unordered_multimap` or between `unordered_set` and
  `unordered_multiset` yet. That will hopefully be in the next version of
  Boost.

== Release 1.63.0

* Check hint iterator in `insert`/`emplace_hint`.
* Fix some warnings, mostly in the tests.
* Manually write out `emplace_args` for small numbers of arguments -
  should make template error messages a little more bearable.
* Remove superfluous use of `boost::forward` in emplace arguments,
  which fixes emplacing string literals in old versions of Visual {cpp}.
* Fix an exception safety issue in assignment. If bucket allocation
  throws an exception, it can overwrite the hash and equality functions while
  leaving the existing elements in place. This would mean that the function
  objects wouldn't match the container elements, so elements might be in the
  wrong bucket and equivalent elements would be incorrectly handled.
* Various reference documentation improvements.
* Better allocator support ({svn-ticket-url}/12459[#12459^]).
* Make the no argument constructors implicit.
* Implement missing allocator aware constructors.
* Fix assigning the hash/key equality functions for empty containers.
* Remove unary/binary_function from the examples in the documentation.
  They are removed in {cpp}17.
* Support 10 constructor arguments in emplace. It was meant to support up to 10
  arguments, but an off by one error in the preprocessor code meant it only
  supported up to 9.

== Release 1.62.0

* Remove use of deprecated `boost::iterator`.
* Remove `BOOST_NO_STD_DISTANCE` workaround.
* Remove `BOOST_UNORDERED_DEPRECATED_EQUALITY` warning.
* Simpler implementation of assignment, fixes an exception safety issue
  for `unordered_multiset` and `unordered_multimap`. Might be a little slower.
* Stop using return value SFINAE which some older compilers have issues
  with.

== Release 1.58.0

* Remove unnecessary template parameter from const iterators.
* Rename private `iterator` typedef in some iterator classes, as it
  confuses some traits classes.
* Fix move assignment with stateful, propagate_on_container_move_assign
  allocators ({svn-ticket-url}/10777[#10777^]).
* Fix rare exception safety issue in move assignment.
* Fix potential overflow when calculating number of buckets to allocate
  ({github-pr-url}/4[GitHub #4^]).

== Release 1.57.0

* Fix the `pointer` typedef in iterators ({svn-ticket-url}/10672[#10672^]).
* Fix Coverity warning
  ({github-pr-url}/2[GitHub #2^]).

== Release 1.56.0

* Fix some shadowed variable warnings ({svn-ticket-url}/9377[#9377^]).
* Fix allocator use in documentation ({svn-ticket-url}/9719[#9719^]).
* Always use prime number of buckets for integers. Fixes performance
  regression when inserting consecutive integers, although makes other
  uses slower ({svn-ticket-url}/9282[#9282^]).
* Only construct elements using allocators, as specified in {cpp}11 standard.

== Release 1.55.0

* Avoid some warnings ({svn-ticket-url}/8851[#8851^], {svn-ticket-url}/8874[#8874^]).
* Avoid exposing some detail functions via. ADL on the iterators.
* Follow the standard by only using the allocators' construct and destroy
  methods to construct and destroy stored elements. Don't use them for internal
  data like pointers.

== Release 1.54.0

* Mark methods specified in standard as `noexpect`. More to come in the next
  release.
* If the hash function and equality predicate are known to both have nothrow
  move assignment or construction then use them.

== Release 1.53.0

* Remove support for the old pre-standard variadic pair constructors, and
  equality implementation. Both have been deprecated since Boost 1.48.
* Remove use of deprecated config macros.
* More internal implementation changes, including a much simpler
  implementation of `erase`.

== Release 1.52.0

* Faster assign, which assigns to existing nodes where possible, rather than
  creating entirely new nodes and copy constructing.
* Fixed bug in `erase_range` ({svn-ticket-url}/7471[#7471^]).
* Reverted some of the internal changes to how nodes are created, especially
  for {cpp}11 compilers. 'construct' and 'destroy' should work a little better
  for {cpp}11 allocators.
* Simplified the implementation a bit. Hopefully more robust.

== Release 1.51.0

* Fix construction/destruction issue when using a {cpp}11 compiler with a
  {cpp}03 allocator ({svn-ticket-url}/7100[#7100^]).
* Remove a `try..catch` to support compiling without exceptions.
* Adjust SFINAE use to try to support g++ 3.4 ({svn-ticket-url}/7175[#7175^]).
* Updated to use the new config macros.

== Release 1.50.0

* Fix equality for `unordered_multiset` and `unordered_multimap`.
* {svn-ticket-url}/6857[Ticket 6857^]:
  Implement `reserve`.
* {svn-ticket-url}/6771[Ticket 6771^]:
  Avoid gcc's `-Wfloat-equal` warning.
* {svn-ticket-url}/6784[Ticket 6784^]:
  Fix some Sun specific code.
* {svn-ticket-url}/6190[Ticket 6190^]:
  Avoid gcc's `-Wshadow` warning.
* {svn-ticket-url}/6905[Ticket 6905^]:
  Make namespaces in macros compatible with `bcp` custom namespaces.
  Fixed by Luke Elliott.
* Remove some of the smaller prime number of buckets, as they may make
  collisions quite probable (e.g. multiples of 5 are very common because
  we used base 10).
* On old versions of Visual {cpp}, use the container library's implementation
  of `allocator_traits`, as it's more likely to work.
* On machines with 64 bit std::size_t, use power of 2 buckets, with Thomas
  Wang's hash function to pick which one to use. As modulus is very slow
  for 64 bit values.
* Some internal changes.

== Release 1.49.0

* Fix warning due to accidental odd assignment.
* Slightly better error messages.

== Release 1.48.0 - Major update

This is major change which has been converted to use Boost.Move's move
emulation, and be more compliant with the {cpp}11 standard. See the
xref:unordered.adoc#compliance[compliance section] for details.

The container now meets {cpp}11's complexity requirements, but to do so
uses a little more memory. This means that `quick_erase` and
`erase_return_void` are no longer required, they'll be removed in a
future version.

{cpp}11 support has resulted in some breaking changes:

* Equality comparison has been changed to the {cpp}11 specification.
  In a container with equivalent keys, elements in a group with equal
  keys used to have to be in the same order to be considered equal,
  now they can be a permutation of each other. To use the old
  behavior define the macro `BOOST_UNORDERED_DEPRECATED_EQUALITY`.

* The behaviour of swap is different when the two containers to be
  swapped has unequal allocators. It used to allocate new nodes using
  the appropriate allocators, it now swaps the allocators if
  the allocator has a member structure `propagate_on_container_swap`,
  such that `propagate_on_container_swap::value` is true.

* Allocator's `construct` and `destroy` functions are called with raw
  pointers, rather than the allocator's `pointer` type.

* `emplace` used to emulate the variadic pair constructors that
  appeared in early {cpp}0x drafts. Since they were removed it no
  longer does so. It does emulate the new `piecewise_construct`
  pair constructors - only you need to use
  `boost::piecewise_construct`. To use the old emulation of
  the variadic constructors define
  `BOOST_UNORDERED_DEPRECATED_PAIR_CONSTRUCT`.

== Release 1.45.0

* Fix a bug when inserting into an `unordered_map` or `unordered_set` using
  iterators which returns `value_type` by copy.

== Release 1.43.0

* {svn-ticket-url}/3966[Ticket 3966^]:
  `erase_return_void` is now `quick_erase`, which is the
  http://home.roadrunner.com/~hinnant/issue_review/lwg-active.html#579[
  current forerunner for resolving the slow erase by iterator^], although
  there's a strong possibility that this may change in the future. The old
  method name remains for backwards compatibility but is considered deprecated
  and will be removed in a future release.
* Use Boost.Exception.
* Stop using deprecated `BOOST_HAS_*` macros.

== Release 1.42.0

* Support instantiating the containers with incomplete value types.
* Reduced the number of warnings (mostly in tests).
* Improved codegear compatibility.
* {svn-ticket-url}/3693[Ticket 3693^]:
  Add `erase_return_void` as a temporary workaround for the current
  `erase` which can be inefficient because it has to find the next
  element to return an iterator.
* Add templated find overload for compatible keys.
* {svn-ticket-url}/3773[Ticket 3773^]:
  Add missing `std` qualifier to `ptrdiff_t`.
* Some code formatting changes to fit almost all lines into 80 characters.

== Release 1.41.0 - Major update

* The original version made heavy use of macros to sidestep some of the older
  compilers' poor template support. But since I no longer support those
  compilers and the macro use was starting to become a maintenance burden it
  has been rewritten to use templates instead of macros for the implementation
  classes.

* The container object is now smaller thanks to using `boost::compressed_pair`
  for EBO and a slightly different function buffer - now using a bool instead
  of a member pointer.

* Buckets are allocated lazily which means that constructing an empty container
  will not allocate any memory.

== Release 1.40.0

* {svn-ticket-url}/2975[Ticket 2975^]:
  Store the prime list as a preprocessor sequence - so that it will always get
  the length right if it changes again in the future.
* {svn-ticket-url}/1978[Ticket 1978^]:
  Implement `emplace` for all compilers.
* {svn-ticket-url}/2908[Ticket 2908^],
  {svn-ticket-url}/3096[Ticket 3096^]:
  Some workarounds for old versions of borland, including adding explicit
  destructors to all containers.
* {svn-ticket-url}/3082[Ticket 3082^]:
  Disable incorrect Visual {cpp} warnings.
* Better configuration for {cpp}0x features when the headers aren't available.
* Create less buckets by default.

== Release 1.39.0

* {svn-ticket-url}/2756[Ticket 2756^]: Avoid a warning
  on Visual {cpp} 2009.
* Some other minor internal changes to the implementation, tests and
  documentation.
* Avoid an unnecessary copy in `operator[]`.
* {svn-ticket-url}/2975[Ticket 2975^]: Fix length of
  prime number list.

== Release 1.38.0

* Use link:../../../core/swap.html[`boost::swap`^].
* {svn-ticket-url}/2237[Ticket 2237^]:
  Document that the equality and inequality operators are undefined for two
  objects if their equality predicates aren't equivalent. Thanks to Daniel
  Krügler.
* {svn-ticket-url}/1710[Ticket 1710^]:
  Use a larger prime number list. Thanks to Thorsten Ottosen and Hervé
  Brönnimann.
* Use
  link:../../../type_traits/index.html[aligned storage^] to store the types.
  This changes the way the allocator is used to construct nodes. It used to
  construct the node with two calls to the allocator's `construct`
  method - once for the pointers and once for the value. It now constructs
  the node with a single call to construct and then constructs the value using
  in place construction.
* Add support for {cpp}0x initializer lists where they're available (currently
  only g++ 4.4 in {cpp}0x mode).

== Release 1.37.0

* Rename overload of `emplace` with hint, to `emplace_hint` as specified in
  http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2008/n2691.pdf[n2691^].
* Provide forwarding headers at `<boost/unordered/unordered_map_fwd.hpp>` and
  `<boost/unordered/unordered_set_fwd.hpp>`.
* Move all the implementation inside `boost/unordered`, to assist
  modularization and hopefully make it easier to track Release subversion.

== Release 1.36.0

First official release.

* Rearrange the internals.
* Move semantics - full support when rvalue references are available, emulated
  using a cut down version of the Adobe move library when they are not.
* Emplace support when rvalue references and variadic template are available.
* More efficient node allocation when rvalue references and variadic template
  are available.
* Added equality operators.

== Boost 1.35.0 Add-on - 31st March 2008

Unofficial release uploaded to vault, to be used with Boost 1.35.0. Incorporated
many of the suggestions from the review.

* Improved portability thanks to Boost regression testing.
* Fix lots of typos, and clearer text in the documentation.
* Fix floating point to `std::size_t` conversion when calculating sizes from
  the max load factor, and use `double` in the calculation for greater accuracy.
* Fix some errors in the examples.

== Review Version

Initial review version, for the review conducted from 7th December 2007 to
16th December 2007.


