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## Change Log

### Review Version

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

### 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.

### Boost 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 1.37.0

- Rename overload of `emplace` with hint, to `emplace_hint` as specified in 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 changes in subversion.

### Boost 1.38.0

- Use `boost::swap`.
- 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.
- Ticket 1710: Use a larger prime number list. Thanks to Thorsten Ottosen and Hervé Brönnimann.
- Use 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 C++0x initializer lists where they're available (currently only g++ 4.4 in C++0x mode).

### Boost 1.39.0

- Ticket 2756: Avoid a warning on Visual C++ 2009.
- Some other minor internal changes to the implementation, tests and documentation.
- Avoid an unnecessary copy in `operator[]`.
- Ticket 2975: Fix length of prime number list.

### Boost 1.40.0

- 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.
- Ticket 1978: Implement `emplace` for all compilers.
- Ticket 2908, Ticket 3096: Some workarounds for old versions of borland, including adding explicit destructors to all containers.
- Ticket 3082: Disable incorrect Visual C++ warnings.
- Better configuration for C++0x features when the headers aren't available.
- Create less buckets by default.

### Boost 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.

### Boost 1.42.0

- Support instantiating the containers with incomplete value types.
- Reduced the number of warnings (mostly in tests).
- Improved codegear compatibility.
- 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.
- Ticket 3773: Add missing `std` qualifier to `ptrdiff_t`.
- Some code formatting changes to fit almost all lines into 80 characters.

### Boost 1.43.0

- Ticket 3966: `erase_return_void` is now `quick_erase`, which is the 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.

### Boost 1.45.0

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

### Boost 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 C++11 standard. See the compliance section for details.

The container now meets C++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.

C++11 support has resulted in some breaking changes:

- Equality comparison has been changed to the C++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 C++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`.

### Boost 1.49.0

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

### Boost 1.50.0

- Fix equality for `unordered_multiset` and `unordered_multimap`.
- Ticket 6857: Implement `reserve`.
- Ticket 6771: Avoid gcc's `-Wfloat-equal` warning.
- Ticket 6784: Fix some Sun specific code.
- Ticket 6190: Avoid gcc's `-Wshadow` warning.
- 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 C++, 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.

### Boost 1.51.0

- Fix construction/destruction issue when using a C++11 compiler with a C++03 allocator (#7100).
- Remove a `try..catch` to support compiling without exceptions.
- Adjust SFINAE use to try to support g++ 3.4 (#7175).
- Updated to use the new config macros.

### Boost 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` (#7471).
- Reverted some of the internal changes to how nodes are created, especially for C++11 compilers. 'construct' and 'destroy' should work a little better for C++11 allocators.
- Simplified the implementation a bit. Hopefully more robust.

### Boost 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`.

### Boost 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.

### Boost 1.55.0

- Avoid some warnings (#8851, #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.

### Boost 1.56.0

- Fix some shadowed variable warnings (#9377).
- Fix allocator use in documentation (#9719).
- Always use prime number of buckets for integers. Fixes performance regression when inserting consecutive integers, although makes other uses slower (#9282).
- Only construct elements using allocators, as specified in C++11 standard.

### Boost 1.57.0

- Fix the `pointer` typedef in iterators (#10672).
- Fix Coverity warning (GitHub #2).

### Boost 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 (#10777).
- Fix rare exception safety issue in move assignment.
- Fix potential overflow when calculating number of buckets to allocate (GitHub #4).

### Boost 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.

### Boost 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 C++.
- 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 (#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 C++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.

### Boost 1.64.0

- Initial support for new C++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.

### Boost 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.

### Boost 1.66.0

- Simpler move construction implementation.
- Documentation fixes (GitHub #6).

### Boost 1.67.0

- Improved C++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 C++20 support:
  - Use `boost::to_address`, which has the proposed C++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 C++, 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 C++17, thanks to Daniela Engert (PR#7).
- Stop using `BOOST_DEDUCED_TYPENAME`.
- Update some Boost include paths.
- Rename some internal methods, and variables.
- Various testing improvements.
- Miscellaneous internal changes.