[/
 / Copyright (c) 2009-2020 Ion Gaztañaga
 /
 / Distributed under the Boost Software License, Version 1.0. (See accompanying
 / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 /]

[library Boost.Container
    [quickbook 1.7]
    [authors [Gaztanaga, Ion]]
    [copyright 2009-2026 Ion Gaztanaga]
    [id container]
    [dirname container]
    [purpose Containers library]
    [license
        Distributed under the Boost Software License, Version 1.0.
        (See accompanying file LICENSE_1_0.txt or copy at
        [@http://www.boost.org/LICENSE_1_0.txt])
    ]
]

[template super[x]'''<superscript>'''[x]'''</superscript>''']
[template sub[x]'''<subscript>'''[x]'''</subscript>''']

[section:intro Introduction]

[*Boost.Container] library implements several well-known containers, including
STL containers. The aim of the library is to offer advanced features not present
in standard containers or to offer the latest standard draft features for compilers
that don't comply with the latest C++ standard.

In short, what does [*Boost.Container] offer?

* Access to many of the latest C++ standard features and have an easy code migration when you change your compiler.
* A portable, high performance implementation that works when compiling without exceptions support and
  offers customized error handling when a container needs to signal an exceptional error.
* Users obtain a more uniform performance across all plataforms,
  including [link container.unique_features.scary_iterators SCARY iterators].
* Userful polymorphic allocators and memory resources, including implementation and emulation for pre-C++17 compilers
* New advanced features (e.g. recursive containers) and [link container.configurable_containers configurability options for containers].
* Containers support stateful allocators and are compatible with [*Boost.Interprocess]
  (they can be safely placed in shared memory) offering improved performance vs standard containers when using Boost.Interprocess.
* You have very useful non-standard containers like `[stable/static/small]_vector`, `flat_[multi]set/map`, `devector` or `segtor`.
* If you work on multiple platforms, you'll have a portable behaviour without depending
  on the std-lib implementation conformance for each platform. Some examples:
* [link container.extended_functionality Extended functionality] beyond the standard based
   on user feedback to improve code performance.
* [link container.configurable_containers Configuration options] that allow tweaking containers to fit users needs.
* The library offers new useful containers:
  * [classref boost::container::flat_map flat_map],
    [classref boost::container::flat_set flat_set],
    [classref boost::container::flat_multimap flat_multimap] and
    [classref boost::container::flat_multiset flat_multiset]: drop-in
    replacements for standard associative containers but more memory friendly and with faster
    searches.
  * [classref boost::container::stable_vector stable_vector]: a std::list and std::vector hybrid
    container: vector-like random-access iterators and list-like iterator stability in insertions and erasures.
  * [classref boost::container::static_vector static_vector]: a vector-like container that internally embeds
    (statically allocates) all needed memory up to the maximum capacity. Maximum capacity can't be increased and
    it's specified at compile time.
  * [classref boost::container::small_vector small_vector]: a vector-like container that internally embeds
    (statically allocates) a minimum amount of memory, but dynamically allocates elements when capacity
    has to be increased. This minimum capacity is specified at compile time.
  * [classref boost::container::devector devector]: is a hybrid of the standard vector and deque containers.
    It offers cheap (amortized constant time) insertion at both the front and back ends.
  * [classref boost::container::segtor segtor]: a sequence container with segmented
    (block-based) storage like deque but only growth at the back; constant-time push_back/pop_back, random access.
  * [classref boost::container::slist slist]: the classic pre-standard singly linked list implementation
    offering constant-time `size()`. Note that C++11 `forward_list` has no `size()`.

[section:introduction_building_container Building Boost.Container]

There is no need to compile [*Boost.Container], since it's a header-only library,
just include your Boost header directory in your compiler include path *except if you use*:

*  [link container.extended_allocators Extended Allocators]
*  Some [link container.cpp_conformance.polymorphic_memory_resources Polymorphic Memory Resources] classes.
   
Those exceptions are are implemented as a separately compiled library, so in those cases you must install binaries
in a location that can be found by your linker.
If you followed the [@http://www.boost.org/doc/libs/release/more/getting_started/index.html Boost Getting Started]
instructions, that's already been done for you.

[endsect]

[section:tested_compilers Tested compilers]

[*Boost.Container] requires a decent C++03 compatibility. Some compilers known to work are:

*  Visual C++ >= 10.0
*  GCC >= 4.8

[endsect]

[endsect]

[section:unique_features Unique features]

[section:containers_of_incomplete_types Containers of Incomplete Types]

Incomplete types allow
[@http://en.wikipedia.org/wiki/Type_erasure [*type erasure ]] and
[@http://en.wikipedia.org/wiki/Recursive_data_type [*recursive data types]], and
C and C++ programmers have been using it for years to build complex data structures, like
tree structures where a node may have an arbitrary number of children.

What about standard containers? Containers of incomplete types have been under discussion for a long time,
as explained in Matt Austern's great article ([@http://drdobbs.com/184403814 [*The Standard Librarian: Containers of Incomplete Types]]):

["['Unlike most of my columns, this one is about something you can't do with the C++ Standard library:
put incomplete types in one of the standard containers. This column explains why you might want to
do this, why the standardization committee banned it even though they knew it was useful, and what
you might be able to do to get around the restriction.]]

["['In 1997, shortly before the C++ Standard was completed, the standardization committee received a
query: Is it possible to create standard containers with incomplete types? It took a while for the
committee to understand the question. What would such a thing even mean, and why on earth would you
ever want to do it? The committee eventually worked it out and came up with an answer to the question.
(Just so you don't have to skip ahead to the end, the answer is "no.") But the question is much more
interesting than the answer: it points to a useful, and insufficiently discussed, programming technique.
The standard library doesn't directly support that technique, but the two can be made to coexist.]]

["['In a future revision of C++, it might make sense to relax the restriction on instantiating
standard library templates with incomplete types. Clearly, the general prohibition should stay
in place - instantiating templates with incomplete types is a delicate business, and there are
too many classes in the standard library where it would make no sense. But perhaps it should be
relaxed on a case-by-case basis, and `vector` looks like a good candidate for such special-case
treatment: it's the one standard container class where there are good reasons to instantiate
it with an incomplete type and where Standard Library implementors want to make it work. As of
today, in fact, implementors would have to go out of their way to prohibit it!]]

C++11 standard is also cautious about incomplete types and STL: ["['17.6.4.8 Other functions (...) 2.
the effects are undefined in the following cases: (...) In particular - if an incomplete type (3.9)
is used as a template argument when instantiating a template component,
unless specifically allowed for that component]].

Finally C++17 added support for incomplete types in `std::vector`, `std::list` and `std::forward_list`
(see [@https://wg21.link/n4510 ['N4510: Minimal incomplete type support for standard containers, revision 4]]
for details), but no other containers like `std::set/map/unordered_set/unordered_map`, 

Fortunately all [*Boost.Container] containers except
[classref boost::container::static_vector static_vector],
[classref boost::container::small_vector small_vector] and
[classref boost::container::basic_string basic_string] are designed to support incomplete types.
[classref boost::container::static_vector static_vector] and 
[classref boost::container::small_vector small_vector] are special because
they statically allocates memory for `value_type` and this requires complete types.
[classref boost::container::basic_string basic_string] implements Small String Optimization which
also requires complete types.

[*Boost.Container] containers supporting incomplete types also support instantiating iterators to
those incomplete elements.

[section:recursive_containers Recursive containers]

Most [*Boost.Container] containers can be used to define recursive containers:

[import ../example/doc_recursive_containers.cpp]
[doc_recursive_containers]

[endsect]

[section:type_erasure Type Erasure]

Containers of incomplete types are useful to break header file dependencies and improve
compilation types. With Boost.Container, you can write a header file defining a class
with containers of incomplete types as data members, if you carefully put all the
implementation details that require knowing the size of the `value_type` in your
implementation file:

[import ../example/doc_type_erasure.cpp]

In this header file we define a class (`MyClassHolder)` that holds a `vector` of an
incomplete type (`MyClass`) that it's only forward declared.

[doc_type_erasure_MyClassHolder_h]

Then we can define `MyClass` in its own header file.

[doc_type_erasure_MyClass_h]

And include it only in the implementation file of `MyClassHolder`

[doc_type_erasure_MyClassHolder_cpp]

Finally, we can just compile, link, and run!

[doc_type_erasure_main_cpp]

[endsect]

[endsect]

[section:scary_iterators SCARY iterators]

The paper N2913, titled [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2913.pdf
SCARY Iterator Assignment and Initialization], proposed a requirement that a standard container's
iterator types have no dependency on any type argument apart from the container's `value_type`,
`difference_type`, `pointer type`, and `const_pointer` type. In particular, according to the proposal,
the types of a standard container's iterators should not depend on the container's `key_compare`,
`hasher`, `key_equal`, or `allocator` types.

That paper demonstrated that SCARY operations were crucial to the performant implementation of common
design patterns using STL components. It showed that implementations that support SCARY operations reduce
object code bloat by eliminating redundant specializations of iterator and algorithm templates.

[*Boost.Container] containers implement SCARY iterators so the iterator type of a container is only dependent
on the `allocator_traits<allocator_type>::pointer` type (the pointer type of the `value_type` to be inserted
in the container). Reference types and all other typedefs are deduced from the pointer type using the
C++11 `pointer_traits` utility. This leads to lower code bloat in algorithms and classes templated on
iterators.

[endsect]

[section:exception_handling C++ exception handling]

In some environments, such as game development or embedded systems, C++ exceptions are disabled or a customized error handling is needed.
According to document [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2271.html N2271 EASTL -- Electronic Arts Standard Template Library]
exceptions can be disabled for several reasons:

*  ["['Exception handling incurs some kind of cost in all compiler implementations, including those that avoid
   the cost during normal execution. However, in some cases this cost may arguably offset the cost of the code that it is replacing.]]
*  ["['Exception handling is often agreed to be a superior solution for handling a large range of function return values. However,
   avoiding the creation of functions that need large ranges of return values is superior to using exception handling to handle such values.]]
*  ["['Using exception handling correctly can be difficult in the case of complex software.]]
*  ["['The execution of throw and catch can be significantly expensive with some implementations.]]
*  ["['Exception handling violates the don't-pay-for-what-you-don't-use design of C++, as it incurs overhead in any non-leaf function that
   has destructible stack objects regardless of whether they use exception handling.]]
*  ["['The approach that game software usually takes is to avoid the need for exception handling where possible; avoid the possibility
   of circumstances that may lead to exceptions. For example, verify up front that there is enough memory for a subsystem to do its job
   instead of trying to deal with the problem via exception handling or any other means after it occurs.]]
*  ["['However, some game libraries may nevertheless benefit from the use of exception handling. It's best, however,
   if such libraries keep the exception handling internal lest they force their usage of exception handling on the rest of the application.]]

In order to support environments without C++ exception support or environments with special error handling needs,
[*Boost.Container] changes error signalling behaviour when `BOOST_CONTAINER_USER_DEFINED_THROW_CALLBACKS` or `BOOST_NO_EXCEPTIONS`
is defined. The former shall be defined by the user and the latter can be either defined by the user or implicitly defined by [*Boost.Confg]
when the compiler has been invoked with the appropriate flag (like `-fno-exceptions` in GCC).

When dealing with user-defined classes, (e.g. when constructing user-defined classes):

*  If `BOOST_NO_EXCEPTIONS` is defined, the library avoids using `try`/`catch`/`throw` statements. The class writer must handle and
   propagate error situations internally as no error will be propagated through [*Boost.Container].
*  If `BOOST_NO_EXCEPTIONS` is *not* defined, the library propagates exceptions offering the exception guarantees detailed in the documentation.

When the library needs to throw an exception (such as `out_of_range` when an incorrect index is used in `vector::at`), the library calls
a throw-callback declared in [headerref boost/container/throw_exception.hpp]:

*  If `BOOST_CONTAINER_USER_DEFINED_THROW_CALLBACKS` is defined, then the programmer must provide its own definition for all
   `throw_xxx` functions. Those functions can't return, they must throw an exception or call `std::exit` or `std::abort`.
*  Else if `BOOST_NO_EXCEPTIONS` is defined, a `BOOST_ASSERT_MSG` assertion is triggered
   (see [@http://www.boost.org/libs/utility/assert.html Boost.Assert] for more information).
   If this assertion returns, then `std::abort` is called.
*  Else, an appropriate standard library exception is thrown (like `std::out_of_range`).

[endsect]

[section:other_features Other features]

* Default constructors don't allocate memory which improves performance and
  usually implies a no-throw guarantee (if predicate's or allocator's default constructor doesn't throw).

* Small string optimization for [classref boost::container::basic_string basic_string],
  with an internal buffer of 11/23 bytes (32/64 bit systems)
  [*without] increasing the usual `sizeof` of the string (3 words).

* `[multi]set/map` containers are size optimized embedding the color bit of the red-black tree nodes
   in the parent pointer.

* `[multi]set/map` containers use no recursive functions so stack problems are avoided.

[endsect]

[endsect]

[section:non_standard_containers Non-standard containers]

[section:stable_vector ['stable_vector]]

This useful, fully STL-compliant stable container [@http://bannalia.blogspot.com/2008/09/introducing-stablevector.html designed by Joaqu\u00EDn M. L\u00F3pez Mu\u00F1oz]
is an hybrid between `vector` and `list`, providing most of
the features of `vector` except [@http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#69 element contiguity].

Extremely convenient as they are, `vector`s have a limitation that many novice C++ programmers frequently stumble upon:
iterators and references to an element of an `vector` are invalidated when a preceding element is erased or when the
vector expands and needs to migrate its internal storage to a wider memory region (i.e. when the required size exceeds
the vector's capacity). We say then that `vector`s are unstable: by contrast, stable containers are those for which
references and iterators to a given element remain valid as long as the element is not erased: examples of stable containers
within the C++ standard library are `list` and the standard associative containers (`set`, `map`, etc.).

Sometimes stability is too precious a feature to live without, but one particular property of `vector`s, element contiguity,
makes it impossible to add stability to this container. So, provided we sacrifice element contiguity, how much
can a stable design approach the behavior of `vector` (random access iterators, amortized constant time end
insertion/deletion, minimal memory overhead, etc.)?
The following image describes the layout of a possible data structure upon which to base the design of a stable vector:

[$../../libs/container/doc/images/stable_vector.png  [width 50%] [align center] ]

Each element is stored in its own separate node. All the nodes are referenced from a contiguous array of pointers, but
also every node contains an "up" pointer referring back to the associated array cell. This up pointer is the key element
to implementing stability and random accessibility:

Iterators point to the nodes rather than to the pointer array. This ensures stability, as it is only the pointer array
that needs to be shifted or relocated upon insertion or deletion. Random access operations can be implemented by using
the pointer array as a convenient intermediate zone. For instance, if the iterator it holds a node pointer `it.p` and we
want to advance it by n positions, we simply do:

[c++]

   it.p = *(it.p->up+n);

That is, we go "up" to the pointer array, add n there and then go "down" to the resulting node.

[*General properties]. [classref boost::container::stable_vector stable_vector] satisfies all the requirements of a container, a reversible container and a sequence
and provides all the optional operations present in vector. Like vector, iterators are random access. [classref boost::container::stable_vector stable_vector]
does not provide element contiguity; in exchange for this absence, the container is stable, i.e. references and iterators
to an element of a [classref boost::container::stable_vector stable_vector] remain valid as long as the element is not erased, and an iterator that has been
assigned the return value of end() always remain valid until the destruction of the associated [classref boost::container::stable_vector stable_vector].

[*Operation complexity]. The big-O complexities of [classref boost::container::stable_vector stable_vector] operations match exactly those of vector. In general,
insertion/deletion is constant time at the end of the sequence and linear elsewhere. Unlike vector, [classref boost::container::stable_vector stable_vector]
does not internally perform any value_type destruction, copy/move construction/assignment operations other than those exactly
corresponding to the insertion of new elements or deletion of stored elements, which can sometimes compensate in terms of
performance for the extra burden of doing more pointer manipulation and an additional allocation per element.

[*Exception safety]. (according to [@http://www.boost.org/community/exception_safety.html Abrahams' terminology])
As [classref boost::container::stable_vector stable_vector] does not internally copy/move elements around, some
operations provide stronger exception safety guarantees than in vector:

[table:stable_vector_req Exception safety
    [[operation] [exception safety for `vector<T>`] [exception safety for [classref boost::container::stable_vector stable_vector]`<T>`]]
    [[insert]    [strong unless copy/move construction/assignment of `T` throw (basic)]     [strong]]
    [[erase]     [no-throw unless copy/move construction/assignment  of `T` throw (basic)]     [no-throw]]
]

[*Memory overhead]. The C++ standard does not specify requirements on memory consumption, but virtually any implementation
of `vector` has the same behavior with respect to memory usage: the memory allocated by a `vector` v with n elements of type T
is

m[sub v] = c\u2219e,

where c is `v.capacity()` and e is `sizeof(T)`. c can be as low as n if the user has explicitly reserved the exact capacity
required; otherwise, the average value c for a growing `vector` oscillates between 1.25\u2219n and 1.5\u2219n for typical resizing
policies. For [classref boost::container::stable_vector stable_vector], the memory usage is

m[sub sv] = (c + 1)p + (n + 1)(e + p),

where p is the size of a pointer. We have c + 1 and n + 1 rather than c and n because a dummy node is needed at the end of
the sequence. If we call f the capacity to size ratio c/n and assume that n is large enough, we have that

m[sub sv]/m[sub v] \u2243 (fp + e + p)/fe.

So, [classref boost::container::stable_vector stable_vector] uses less memory than `vector` only when e > p and the capacity to size ratio exceeds a given threshold:

m[sub sv] < m[sub v] <-> f > (e + p)/(e - p). (provided e > p)

This threshold approaches typical values of f below 1.5 when e > 5p; in a 32-bit architecture, when e > 20 bytes.

[*Summary]. [classref boost::container::stable_vector stable_vector] is a drop-in replacement for `vector` providing stability of references and iterators, in exchange
for missing element contiguity and also some performance and memory overhead. When the element objects are expensive to
move around, the performance overhead can turn into a net performance gain for [classref boost::container::stable_vector stable_vector] if many middle insertions
or deletions are performed or if resizing is very frequent. Similarly, if the elements are large there are situations when
the memory used by [classref boost::container::stable_vector stable_vector] can actually be less than required by vector.

['Note: Text and explanations taken from [@http://bannalia.blogspot.com/2008/09/introducing-stablevector.html Joaqu\u00EDn's blog]]

[endsect]

[section:flat_xxx ['flat_(multi)map/set] associative containers]

Using sorted vectors instead of tree-based associative containers is a well-known technique in
C++ world. Matt Austern's  classic article
[@http://lafstern.org/matt/col1.pdf Why You Shouldn't Use set, and What You Should Use Instead]
(C++ Report 12:4, April 2000) was enlightening:

["['Red-black trees aren't the only way to organize data that permits lookup in logarithmic time.  One of the basic
algorithms of computer science is binary search, which works by successively dividing a range in half. Binary
search is log N and it doesn't require any fancy data structures, just a sorted collection of elements.
(...) You can use whatever data structure is convenient, so long as it provides STL iterator;
usually it's easiest to use a C array, or a vector.]]

["['Both std::lower_bound and set::find take time proportional to log N, but the constants of proportionality
are very different.  Using g++ (...) it takes X seconds to perform a million lookups in a
sorted vector<double> of a million elements, and almost twice as long (...) using a set. Moreover,
the set uses almost three times as much memory (48 million bytes) as the vector (16.8 million).]]

["['Using a sorted vector instead of a set gives you faster lookup and much faster iteration,
but at the cost of slower insertion.  Insertion into a set, using set::insert, is proportional
to log N, but insertion into a sorted vector, (...)
, is proportional to N. Whenever you insert something into a vector,
vector::insert has to make room by shifting all of the elements that follow it.  On average, if you're equally
likely to insert a new element anywhere, you'll be shifting N/2 elements.]]

["['It may sometimes be convenient to bundle all of this together into a small container adaptor.
This class does not satisfy the requirements of a Standard Associative Container, since the complexity of insert is
O(N) rather than O(log N), but otherwise it is almost a drop-in replacement for set.]]

Following Matt Austern's indications, Andrei Alexandrescu's
[@http://www.bestwebbuys.com/Modern-C-Design-Generic-Programming-and-Design-Patterns-Applied-ISBN-9780201704310?isrc=-rd Modern C++ Design]
showed `AssocVector`, a `std::map` drop-in
replacement designed in his [@http://loki-lib.sourceforge.net/ Loki] library:

["['It seems as if we're better off with a sorted vector. The disadvantages of a sorted
vector are linear-time insertions and linear-time deletions (...). In exchange, a vector
offers about twice the lookup speed and a much smaller working set (...).
Loki saves the trouble of maintaining a sorted vector by hand by defining an AssocVector class
template. AssocVector is a drop-in replacement for std::map (it supports the same set of member
functions), implemented on top of std::vector. AssocVector differs from a map in the behavior of
its erase functions (AssocVector::erase invalidates all iterators into the object) and in the
complexity guarantees of insert and erase (linear as opposed to constant). ]]

[*Boost.Container] [classref boost::container::flat_map flat_map], [classref boost::container::flat_set flat_set], [classref boost::container::flat_multimap flat_multimap] and [classref boost::container::flat_multiset flat_multiset] containers are ordered, vector-like container based, associative
containers following  Austern's and Alexandrescu's guidelines. These ordered vector containers have also
benefited with the addition of `move semantics` to C++11, speeding up insertion and
erasure times considerably. Flat associative containers have the following attributes:

* Faster lookup than standard associative containers
* Much faster iteration than standard associative containers.
   Random-access iterators instead of bidirectional iterators.
* Less memory consumption for small objects (and for big objects if `shrink_to_fit` is used)
* Improved cache performance (data is stored in contiguous memory)
* Non-stable iterators (iterators are invalidated when inserting and erasing elements)
* Non-copyable and non-movable values types can't be stored
* Weaker exception safety than standard associative containers
(copy/move constructors can throw when shifting values in erasures and insertions)
* Slower insertion and erasure than standard associative containers (specially for non-movable types)

[endsect]

[section:devector ['devector]]

[classref boost::container::devector devector] is a hybrid of the standard vector and deque containers originally written by Thaler Benedek.
It offers cheap (amortized constant time) insertion at both the front and back ends,
while also providing the regular features of `vector`, in particular the contiguous underlying memory.

Unlike `vector`, [classref boost::container::devector devector] can have free capacity both before and after the elements. This enables efficient
implementation of methods that modify the [classref boost::container::devector devector] at the front. In general, [classref boost::container::devector devector]'s available methods
are a superset of those of `vector` with similar behaviour, barring a couple of iterator invalidation
guarantees that differ.

The static size overhead for boost's [classref boost::container::devector devector] is one extra `size_t` per container: Usually sizeof([classref boost::container::devector devector]) == 4*sizeof(T*).

There are different strategies when elements are to be inserted at one extreme of the container and there is
no room for additional elements at that extreme. One simple strategy would be to reallocate a bigger buffer
and move all elements to the new memory. However, this would lead to unbounded memory waste when elements are
inserted predominantly on one extreme (e.g. pushed at one extreme and popped from the other, like a LIFO pattern).

To avoid unbounded memory waste, Boost.Container's [classref boost::container::devector devector] uses a different strategy:

* If elements are inserted near a extreme and there is free space on that extreme, the insertion is performed
  without any additional data movement (only the elements between the insertion point and the extreme are moved).
  
* If elements are inserted near one extreme and the free space on that extreme is exhausted, all existing elements
  are relocated (moved) to the center of the internal memory buffer. This makes room in the exhausted extreme
  to insert more elements without allocating a new buffer.

* Potentially, the maximum number of possible relocations (movements) reusing the memory buffer are Olog(N),
  but that would lead non-amortized constant-time insertion at the extremes. In consequence, the number of
  relocations must be limited ('relocation limit') and a reallocation (allocation of a new memory buffer) will be
  performed if the load-factor of the container defined as (`size()/length_of_internal_buffer`) surpasses the relocation limit (see
  Lars Greger Nordland Hagen's [@http://larshagencpp.github.io/blog/2016/05/22/devector "Double-ended vector - is it useful?"]
  article for more details).

* This approach offers a reasonable balance between a reasonable memory overhead and performance.

However, this strategy has also some downsides:

* Insertions at the extremes have no strong exception guarantee as data has to be move inside the existing buffer.

* Due to the memory relocation vs reallocation strategy explained above:
    * `capacity()` can no longer tell the maximum number of elements that the container can hold and, at the same time,
        the number of insertions to perform before a reallocation is performed. Depending on which extreme a insertion
        takes place, a reallocation might occur or not (maybe there is free capacity at that extreme)

   * Instead of removing the `capacity()` member or renaming it to "`minimum_capacity()`", the definition has been changed
     to tell the *minimum* number of elements that can be inserted without reallocating. This allows the typical pattern
     where:
        * If `reserve(n)` is called, `capacity() >= n`
        * If `capacity() == n` it is guaranteed that if `size() <= n` no reallocation will occur.

   * However the usual container invariant where `size() <= capacity()` does not hold. `size()` can be bigger than
    `capacity()` because elements can be always inserted at an extreme with free capacity without reallocation.


[endsect]

[section:slist ['slist]]

When the standard template library was designed, it contained a singly linked list called [classref boost::container::slist slist].
Unfortunately, this container was not standardized and remained as an extension for many standard
library implementations until C++11 introduced `forward_list`, which is a bit different from the
the original SGI [classref boost::container::slist slist]. According to [@http://www.sgi.com/tech/stl/Slist.html SGI STL documentation]:

["['An [classref boost::container::slist slist] is a singly linked list: a list where each element is linked to the next element, but
not to the previous element. That is, it is a Sequence that supports forward but not backward traversal,
and (amortized) constant time insertion and removal of elements. Slists, like lists, have the important
property that insertion and splicing do not invalidate iterators to list elements, and that even removal
invalidates only the iterators that point to the elements that are removed. The ordering of iterators
may be changed (that is, [classref boost::container::slist slist]`<T>::iterator` might have a different predecessor or successor after a list
operation than it did before), but the iterators themselves will not be invalidated or made to point to
different elements unless that invalidation or mutation is explicit.]]

["['The main difference between [classref boost::container::slist slist] and list is that list's iterators are bidirectional iterators,
while [classref boost::container::slist slist]'s iterators are forward iterators. This means that [classref boost::container::slist slist] is less versatile than list;
frequently, however, bidirectional iterators are unnecessary. You should usually use [classref boost::container::slist slist] unless
you actually need the extra functionality of list, because singly linked lists are smaller and faster
than double linked lists.]]

["['Important performance note: like every other Sequence, [classref boost::container::slist slist] defines the member functions insert and erase.
Using these member functions carelessly, however, can result in disastrously slow programs. The problem is that
insert's first argument is an iterator pos, and that it inserts the new element(s) before pos. This means that
insert must find the iterator just before pos; this is a constant-time operation for list, since list has
bidirectional iterators, but for [classref boost::container::slist slist] it must find that iterator by traversing the list from the beginning
up to pos. In other words: insert and erase are slow operations anywhere but near the beginning of the [classref boost::container::slist slist].]]

["['Slist provides the member functions insert_after and erase_after, which are constant time operations: you should
always use insert_after and erase_after whenever possible. If you find that insert_after and erase_after aren't
adequate for your needs, and that you often need to use insert and erase in the middle of the list, then you
should probably use list instead of [classref boost::container::slist slist].]]

[*Boost.Container] updates the classic [classref boost::container::slist slist] container with C++11 features like move semantics and placement
insertion and implements it a bit differently than the standard C++ `forward_list`. `forward_list` has no `size()`
method, so it's been designed to allow (or in practice, encourage) implementations without tracking list size
with every insertion/erasure, allowing constant-time
`splice_after(iterator, forward_list &, iterator, iterator)`-based list merging. On the other hand [classref boost::container::slist slist] offers
constant-time `size()` for those that don't care about linear-time `splice_after(iterator, [classref boost::container::slist slist] &, iterator, iterator)`
`size()` and offers an additional `splice_after(iterator, [classref boost::container::slist slist] &, iterator, iterator, size_type)` method that
can speed up [classref boost::container::slist slist] merging when the programmer already knows the size. [classref boost::container::slist slist] and `forward_list` are therefore
complementary.

[endsect]

[section:static_vector ['static_vector]]

[classref boost::container::static_vector static_vector] is an hybrid between `vector` and `array`: like `vector`, it's a sequence container
with contiguous storage that can change in size, along with the static allocation, low overhead,
and fixed capacity of `array`. [classref boost::container::static_vector static_vector] is based on Adam Wulkiewicz and Andrew Hundt's
high-performance [@https://svn.boost.org/svn/boost/sandbox/varray/doc/html/index.html varray]
class.

The number of elements in a [classref boost::container::static_vector static_vector] may vary dynamically up to a fixed capacity
because elements are stored within the object itself similarly to an array. However, objects are
initialized as they are inserted into [classref boost::container::static_vector static_vector] unlike C arrays or `std::array` which must construct
all elements on instantiation. The behavior of [classref boost::container::static_vector static_vector] enables the use of statically allocated
elements in cases with complex object lifetime requirements that would otherwise not be trivially
possible. Some other properties:

* Random access to elements
* Constant time insertion and removal of elements at the end
* Linear time insertion and removal of elements at the beginning or in the middle.

[classref boost::container::static_vector static_vector] is well suited for use in a buffer, the internal implementation of other
classes, or use cases where there is a fixed limit to the number of elements that must be stored.
Embedded and realtime applications where allocation either may not be available or acceptable
are a particular case where [classref boost::container::static_vector static_vector] can be beneficial.

[endsect]

[section:small_vector ['small_vector]]

[classref boost::container::small_vector small_vector] is a vector-like container optimized for the case when it contains few elements.
It contains some preallocated elements in-place, which allows it to avoid the use of dynamic storage allocation
when the actual number of elements is below that preallocated threshold. [classref boost::container::small_vector small_vector] is inspired by
[@http://llvm.org/docs/ProgrammersManual.html#llvm-adt-smallvector-h LLVM's `SmallVector`] container.
Unlike [classref boost::container::static_vector static_vector], [classref boost::container::small_vector small_vector]'s capacity can grow beyond the initial preallocated capacity.

[classref boost::container::small_vector small_vector]`<T, N, Allocator>` is convertible to `small_vector_base<T, Allocator>`, a type that is independent
from the preallocated element count, allowing client code that does not need to be templated on that N argument.
[classref boost::container::small_vector small_vector] inherits all `vector`'s member functions so it supports all standard features like emplacement,
stateful allocators, etc.

[endsect]

[section:segtor ['segtor]]

[classref boost::container::segtor segtor] is a sequence container that supports random access to elements, constant-time insertion and
removal at the end, and linear-time insertion and removal in the middle. It uses the same segmented (block-based)
storage as `deque` but only allows growth at the back: it provides `push_back`, `pop_back`, `emplace_back`, and the
like, but does not provide `push_front`, `pop_front`, or `emplace_front`. In that sense it is the single-ended
counterpart of [classref boost::container::deque deque].

Unlike a single contiguous buffer, segmented storage avoids reallocating and moving all elements when the container
grows: new blocks are allocated as needed. This can reduce peak memory and improve performance when elements are
expensive to move or when growth is large. Inserting or erasing at the end does not invalidate iterators or
references/pointers to existing elements. Insertions and erasures in the middle invalidate iterators and references
in the same way as for `deque`.

The container can be configured via [classref boost::container::segtor_options segtor_options]
to control block size and other parameters.

[endsect]

[endsect]

[section:extended_functionality Extended functionality: Basic extensions]

[section:default_initialialization Default initialization for vector-like containers]

STL and most other containers value initialize new elements in common operations like
`vector::resize(size_type n)` or `explicit vector::vector(size_type n)`.

In some performance-sensitive environments, where vectors are used as a replacement for
variable-size buffers for file or network operations,
[@http://en.cppreference.com/w/cpp/language/value_initialization value initialization]
is a cost that is not negligible as elements are going to be overwritten by an external source
shortly after new elements are added to the container.

[*Boost.Container] offers two new members for `vector`, `static_vector` and `stable_vector`:
`explicit container::container(size_type n, default_init_t)` and
`container::resize(size_type n, default_init_t)`, where new elements are constructed
using [@http://en.cppreference.com/w/cpp/language/default_initialization default initialization].

[endsect]

[section:ordered_range_insertion Ordered range insertion for associative containers (['ordered_unique_range], ['ordered_range]) ]

When filling associative containers big performance gains can be achieved if the input range to be inserted
is guaranteed by the user to be ordered according to the predicate. This can happen when inserting values from a `set` to
a `multiset` or between different associative container families (`[multi]set/map` vs. `flat_[multi]set/map`).

[*Boost.Container] has some overloads for constructors and insertions taking an `ordered_unique_range_t` or
an `ordered_range_t` tag parameters as the first argument. When an `ordered_unique_range_t` overload is used, the
user notifies the container that the input range is ordered according to the container predicate and has no
duplicates. When an `ordered_range_t` overload is used, the
user notifies the container that the input range is ordered according to the container predicate but it might
have duplicates. With this information, the container can avoid multiple predicate calls and improve insertion
times.

[endsect]

[section:constant_time_range_splice Constant-time range splice for `(s)list`]

In the first C++ standard `list::size()` was not required to be constant-time,
and that caused some controversy in the C++ community. Quoting Howard Hinnant's
[@http://howardhinnant.github.io/On_list_size.html ['On List Size]] paper:

[: ['There is a considerable debate on whether `std::list<T>::size()` should be O(1) or O(N).
The usual argument notes that it is a tradeoff with:]

`splice(iterator position, list& x, iterator first, iterator last);`

['If size() is O(1) and this != &x, then this method must perform a linear operation so that it
can adjust the size member in each list]]

C++11 definitely required `size()` to be O(1), so range splice became O(N). However,
Howard Hinnant's paper proposed a new `splice` overload so that even O(1) `list:size()`
implementations could achieve O(1) range splice when the range size was known to the caller:

[: `void splice(iterator position, list& x, iterator first, iterator last, size_type n);`

   [*Effects]: Inserts elements in the range `[first, last)` before position and removes the elements from x.

   [*Requires]: `[first, last)` is a valid range in x. The result is undefined if position is an iterator in the range `[first, last)`. Invalidates only the iterators and references to the spliced elements. `n == distance(first, last)`.

   [*Throws]: Nothing.

   [*Complexity]: Constant time.
]

This new splice signature allows the client to pass the distance of the input range in.
This information is often available at the call site. If it is passed in,
then the operation is constant time, even with an O(1) size.

[*Boost.Container] implements this overload for `list` and a modified version of it for `slist`
(as `slist::size()` is also `O(1)`).

[endsect]

[endsect]

[section:configurable_containers Extended functionality: Configurable containers]

[*Boost.Container] offers the possibility to configure at compile time some parameters of
several containers, apart from the stored type and the allocator. This configuration is passed as
the last template parameter and defined using the utility classes. The following containers can receive
useful configuration options:

[section:configurable_tree_based_associative_containers Configurable tree-based associative ordered containers]

[classref boost::container::set set], [classref boost::container::multiset multiset],
[classref boost::container::map map] and [classref boost::container::multimap multimap] associative containers
are implemented as binary search trees which offer the needed complexity and stability guarantees required by the
C++ standard for associative containers.

[*Boost.Container] offers the possibility to configure at compile time some parameters of the binary search tree
implementation. This configuration is passed as the last template parameter and defined using the utility class
[classref boost::container::tree_assoc_options tree_assoc_options]. The following parameters can be configured:

*  The underlying [*tree implementation] type ([classref boost::container::tree_type tree_type]).
   By default these containers use a red-black tree but the user can use other tree types:
   *  [@http://en.wikipedia.org/wiki/Red%E2%80%93black_tree Red-Black Tree]
   *  [@http://en.wikipedia.org/wiki/Avl_trees AVL tree]
   *  [@http://en.wikipedia.org/wiki/Scapegoat_tree Scapegoat tree]. In this case Insertion and Deletion
      are amortized O(log n) instead of O(log n).
   *  [@http://en.wikipedia.org/wiki/Splay_tree Splay tree]. In this case Searches, Insertions and Deletions
      are amortized O(log n) instead of O(log n).

*  Whether the [*size saving] mechanisms are used to implement the tree nodes
   ([classref boost::container::optimize_size optimize_size]). By default this option is activated and is only
   meaningful to red-black and avl trees (in other cases, this option will be ignored).
   This option will try to put rebalancing metadata inside the "parent" pointer of the node if the pointer
   type has enough alignment. Usually, due to alignment issues, the metadata uses the size of a pointer yielding
   to four pointer size overhead per node, whereas activating this option usually leads to 3 pointer size overhead.
   Although some mask operations must be performed to extract
   data from this special "parent" pointer, in several systems this option also improves performance due to the
   improved cache usage produced by the node size reduction.

See the following example to see how [classref boost::container::tree_assoc_options tree_assoc_options] can be
used to customize these containers:

[import ../example/doc_custom_tree.cpp]
[doc_custom_tree]

[endsect]

[section:configurable_vector Configurable vector]

The configuration for [classref boost::container::vector vector] is passed as
the last template parameter and defined using the utility class
[classref boost::container::vector_options vector_options]. The following parameters can be configured:

*  [classref boost::container::growth_factor growth_factor]: the growth policy of the vector.
   The rate at which the capacity grows is implementation dependent and
   implementations choose exponential growth in order to meet the amortized constant time requirements.
   A higher growth factor will make it faster as it will require less data movement, but it will have a greater memory
   impact (on average, more memory will be unused). A user can provide a custom implementation of the growth factor and some
   predefined policies are available: [classref boost::container::growth_factor_50 growth_factor_50],
   [classref boost::container::growth_factor_60 growth_factor_60] (usually the default in Boost.Container) and
   [classref boost::container::growth_factor_100 growth_factor_100].

*  [classref boost::container::stored_size stored_size]: the type that will be used to store size-related
   parameters inside the vector. Sometimes, when the maximum vector capacity to be used is much less than
   `std::size_t` capacity, it may be beneficial to use a smaller unsigned integer type to represent
   `size()` and `capacity()` values inside the vector, so that the size of an empty vector object is minimized and cache 
   performance is possibly improved. See [classref boost::container::stored_size stored_size] for more details. Note
   that due to alignment issues, using a unsigned type smaller than std::size_t to store size-related parameters might
   not bring any size gains and will severely limit the maximum size of the container.

See the following example to see how [classref boost::container::vector_options vector_options] can be
used to customize `vector`:

[import ../example/doc_custom_vector.cpp]
[doc_custom_vector]

[endsect]

[section:configurable_static_vectors Configurable static vector]

The configuration for [classref boost::container::static_vector static_vector] is passed as
the last template parameter and defined using the utility class
[classref boost::container::static_vector_options static_vector_options]. The following parameters can be configured:

*  [classref boost::container::inplace_alignment inplace_alignment]: the minimum alignment (in bytes) that the stored value type
   needs. This option allows static vectors that need non-default alignments, e.g., to be used in SIMD operations.

*  [classref boost::container::throw_on_overflow throw_on_overflow]: A boolean that specifies if the
   container should throw an exception when the compile-time capacity is not enough to hold the requesteed number
   of objects. When "false", if the capacit is overflowed, the implementation calls to `BOOST_ASSERT` and if that assertion
   does not throw or abort, undefined behavior is triggered.

*  [classref boost::container::stored_size stored_size]: the type that will be used to store size-related
   parameters inside the vector. See `stored_size` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::stored_size stored_size] for more details.

See the following example to see how [classref boost::container::static_vector_options static_vector_options] can be
used to customize `static_vector`:

[import ../example/doc_custom_static_vector.cpp]
[doc_custom_static_vector]

[endsect]

[section:configurable_small_vectors Configurable small vector]

The configuration for [classref boost::container::small_vector small_vector] is passed as
the last template parameter and defined using the utility class
[classref boost::container::small_vector_options small_vector_options]. The following parameters can be configured:

*  [classref boost::container::inplace_alignment inplace_alignment]: the minimum alignment (in bytes) for the in-place storage
   used to build the "small" number of elements. [*The alignment of the dynamic memory must be provided by the allocator
   and it is not affected by this option].

*  [classref boost::container::growth_factor growth_factor]: the growth policy of the vector.
   See `growth_factor` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::growth_factor growth_factor] for more details.

*  [classref boost::container::stored_size stored_size]: the type that will be used to store size-related
   parameters inside the vector. See `stored_size` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::stored_size stored_size] for more details.

See the following example to see how [classref boost::container::small_vector_options small_vector_options] can be
used to customize `small_vector`:

[import ../example/doc_custom_small_vector.cpp]
[doc_custom_small_vector]

[endsect]

[section:configurable_deque Configurable deque / segtor]

The configuration for [classref boost::container::deque deque] / [classref boost::container::segtor segtor]
is passed as the last template parameter and defined using the utility class
[classref boost::container::deque_options deque_options] and [classref boost::container::segtor_options segtor_options] respectively.
The following parameters can be configured:

Parameters that control the size of container's 'block'/'segment' (the container allocates contiguous chunks of elements, called 'blocks'/'segments').
Only one of these paratemers can be specified:

*  [classref boost::container::block_bytes block_bytes]/[classref boost::container::segment_bytes segment_bytes]:
   the number of bytes the container will allocate to store
   elements contiguously: `deque::get_block_size()` will return aproximately `block_bytes/sizeof(value_type)` / `segment_bytes/sizeof(value_type)`.
   A value of zero means the default value.

*  [classref boost::container::block_size block_size]/[classref boost::container::segment_size segment_size]: the number of elements
   the container will allocate contiguously.
   If this option is specified, `deque::get_block_size()` will return the specified `block_size`/`segment_size`.
   A value of zero means the default value.

*  [classref boost::container::stored_size stored_size]: the type that will be used to store size-related
   parameters inside the vector. See `stored_size` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::stored_size stored_size] for more details.

See the following example to see how [classref boost::container::deque_options deque_options] can be
used to customize `deque`:

[import ../example/doc_custom_deque.cpp]
[doc_custom_deque]

See the following example to see how [classref boost::container::segtor_options segtor_options] can be
used to customize `segtor`:

[import ../example/doc_custom_segtor.cpp]
[doc_custom_segtor]

[endsect]

[section:configurable_devector Configurable devector]

The configuration for [classref boost::container::devector devector] is passed as
the last template parameter and defined using the utility class
[classref boost::container::devector_options devector_options]. The following parameters can be configured:

*  [classref boost::container::growth_factor growth_factor]: the growth policy of the vector.
   See `growth_factor` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::growth_factor growth_factor] for more details.

*  [classref boost::container::stored_size stored_size]: the type that will be used to store size-related
   parameters inside the vector. See `stored_size` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::stored_size stored_size] for more details.

*  [classref boost::container::relocate_on_66 relocate_on_XX]: load factor limit that will determine if
   new memory should be allocated or elements should relocated inside existing memory, when the free space
   is exhausted at one end of the container.

See the following example to see how [classref boost::container::devector_options devector_options] can be
used to customize `devector`:

[import ../example/doc_custom_devector.cpp]
[doc_custom_devector]

[endsect]

[section:configurable_string Configurable basic_string]

The configuration for [classref boost::container::basic_string basic_string] is passed as
the last template parameter and defined using the utility class
[classref boost::container::string_options string_options]. The following parameters can be configured:

*  [classref boost::container::growth_factor growth_factor]: the growth policy of the vector.
   See `growth_factor` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::growth_factor growth_factor] for more details.

*  [classref boost::container::stored_size stored_size]: the type that will be used to store size-related
   parameters inside the vector. See `stored_size` option in [link container.configurable_containers.configurable_vector Configurable vector]
   chapter and [classref boost::container::stored_size stored_size] for more details. Note that the internal
   small string optimization buffer might be reduced in size if a smaller than `std::size_t` `stored_size` unsigned
   type is used.

*  [classref boost::container::inline_chars inline_chars]: the number of characters (excluding terminating null) that
   will be stored inside `basic_string` (small string optimization) before using dynamic allocation. Due to internal
   data structure limitations, this value must be equal or less than 127. The implementation will guarantee at least
   that number of characters in the internal buffer, but it might be more depending on alignment issues and the `stored_size`
   option.

See the following example to see how [classref boost::container::string_options string_options] can be
used to customize `string_options`:

[import ../example/doc_custom_string.cpp]
[doc_custom_string]

[endsect]

[endsect]

[section:extended_allocators Extended functionality: Extended allocators]

Many C++ programmers have ever wondered where does good old realloc fit in C++. And that's a good question.
Could we improve [classref boost::container::vector vector] performance using memory expansion mechanisms
to avoid too many copies? But [classref boost::container::vector vector] is not the only container that
could benefit from an improved allocator interface: we could take advantage of the insertion of multiple
elements in [classref boost::container::list list] using a burst allocation mechanism that could amortize
costs (mutex locks, free memory searches...) that can't be amortized when using single node allocation
strategies.

These improvements require extending the STL allocator interface and use make use of a new
general purpose allocator since new and delete don't offer expansion and burst capabilities.

*  [*Boost.Container] containers support an extended allocator interface based on an evolution of proposals
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1953.html N1953: Upgrading the Interface of Allocators using API Versioning],
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2045.html N2045: Improving STL allocators]
and the article
[@../allocplus/index.html Applying classic memory allocation strategies to C++ containers].
The extended allocator interface is implemented by [classref boost::container::allocator allocator],
[classref boost::container::adaptive_pool adaptive_pool] and [classref boost::container::node_allocator node_allocator]
classes.

*  Extended allocators use a modified [@http://g.oswego.edu/dl/html/malloc.html Doug Lea Malloc (DLMalloc)] low-level
allocator and offers an C API to implement memory expansion and burst allocations. DLmalloc is known to be very size
and speed efficient, and this allocator is used as the basis of many malloc implementations, including multithreaded
allocators built above DLmalloc (See [@http://www.malloc.de/en/ ptmalloc2, ptmalloc3] or
[@http://www.nedprod.com/programs/portable/nedmalloc/ nedmalloc]). This low-level allocator is implemented as
a separately compiled library and the following extended allocators depend on the library:

*  [classref boost::container::allocator allocator]: This extended allocator offers expansion, shrink-in place
   and burst allocation capabilities implemented as a thin wrapper around the modified DLMalloc.
   It can be used with all containers and it should be the default choice when the programmer wants to use
   extended allocator capabilities.

*  [classref boost::container::node_allocator node_allocator]: It's a
   [@http://www.boost.org/doc/libs/1_55_0/libs/pool/doc/html/boost_pool/pool/pooling.html#boost_pool.pool.pooling.simple Simple Segregated Storage]
   allocator, similar to [*Boost.Pool] that takes advantage of the modified DLMalloc burst interface. It does not return
   memory to the DLMalloc allocator (and thus, to the system), unless explicitly requested. It does offer a very small
   memory overhead so it's suitable for node containers ([boost::container::list list], [boost::container::slist slist]
   [boost::container::set set]...) that allocate very small `value_type`s and it offers improved node allocation times
   for single node allocations with respecto to [classref boost::container::allocator allocator].

*  [classref boost::container::adaptive_pool adaptive_pool]: It's a low-overhead node allocator that can return memory
   to the system. The overhead can be very low (< 5% for small nodes) and it's nearly as fast as [classref boost::container::node_allocator node_allocator].
   It's also suitable for node containers.

Use them simply specifying the new allocator in the corresponding template argument of your favourite container:

[import ../example/doc_extended_allocators.cpp]
[doc_extended_allocators]

[endsect]

[section:cpp_conformance C++ Conformance]

[*Boost.Container] aims for full C++11 conformance except reasoned deviations,
backporting as much as possible for C++03. Obviously, this conformance is a work
in progress so this section explains what C++ features are implemented and which
of them have been backported to earlier standard conformig compilers.

[section:move_emplace Move and Emplace]

For compilers with rvalue references and for those C++03 types that use
[@http://www.boost.org/libs/move Boost.Move] rvalue reference emulation
[*Boost.Container] supports all C++11 features related to move semantics: containers
are movable, requirements for `value_type` are those specified for C++11 containers.

For compilers with variadic templates, [*Boost.Container] supports placement insertion
(`emplace`, ...) functions from C++11. For those compilers without variadic templates
support [*Boost.Container] uses the preprocessor to create a set of overloads up to
a finite number of parameters.

[endsect]

[section:stateful_allocators Stateful allocators and uses-allocator protocol]

C++03 was not stateful-allocator friendly. For compactness of container objects and for
simplicity, it did not require containers to support allocators with state: Allocator objects
need not be stored in container objects. It was not possible to store an allocator with state,
say an allocator that holds a pointer to an arena from which to allocate. C++03 allowed implementors
to suppose two allocators of the same type always compare equal (that means that memory allocated
by one allocator object could be deallocated by another instance of the same type) and
allocators were not swapped when the container was swapped.

C++11 further improves stateful allocator support through:

* [@http://en.cppreference.com/w/cpp/memory/allocator_traits `std::allocator_traits`].
`std::allocator_traits` is the protocol between a container and an allocator, and
an allocator writer can customize its behaviour (should the container propagate it in
move constructor, swap, etc.?) following `allocator_traits` requirements. [*Boost.Container]
not only supports this model with C++11 but also [*backports it to C++03] via
[classref boost::container::allocator_traits boost::container::allocator_traits] including some
C++17 changes. This class
offers some workarounds for C++03 compilers to achieve the same allocator guarantees as
`std::allocator_traits`.

* [@https://en.cppreference.com/w/cpp/memory/uses_allocator.html `The uses-allocator protocol`]
   allows types to declare they can work with allocators, even when constructed through intermediary
   code that doesn't know about them. [*Boost.Container] implements the trait
   [classref boost::container::uses_allocator uses_allocator] and also implements utilities inspired
   by C++20's additions:
   [funcref boost::container::uninitialized_construct_using_allocator uninitialized_construct_using_allocator]
   and [funcref boost::container::make_obj_using_allocator make_obj_using_allocator].

[endsect]

[section:scoped_allocator Scoped allocators]

C++11 improves stateful allocators with the introduction of
[@http://en.cppreference.com/w/cpp/memory/scoped_allocator_adaptor `std::scoped_allocator_adaptor`]
class template. `scoped_allocator_adaptor` is instantiated with one outer allocator and zero or more inner
allocators.

A scoped allocator is a mechanism to automatically propagate the state of the allocator to the subobjects
of a container in a controlled way. If instantiated with only one allocator type, the inner allocator
becomes the `scoped_allocator_adaptor` itself, thus using the same allocator
resource for the container and every element within the container and, if the elements themselves are
containers, each of their elements recursively. If instantiated with more than one allocator, the first allocator
is the outer allocator for use by the container, the second allocator is passed to the constructors of the
container's elements, and, if the elements themselves are containers, the third allocator is passed to the
elements' elements, and so on.

[*Boost.Container] implements its own [classref boost::container::scoped_allocator_adaptor scoped_allocator_adaptor]
class and [*backports this feature also
to C++03 compilers]. Due to C++03 limitations, in those compilers
the allocator propagation implemented by `scoped_allocator_adaptor::construct` functions
will be based on traits ([classref boost::container::constructible_with_allocator_suffix constructible_with_allocator_suffix]
and [classref boost::container::constructible_with_allocator_prefix constructible_with_allocator_prefix])
proposed in [@http://www.open-std.org/jtc1/sc22/WG21/docs/papers/2008/n2554.pdf
N2554: The Scoped Allocator Model (Rev 2) proposal]. In conforming C++11 compilers or compilers supporting SFINAE
expressions (when `BOOST_NO_SFINAE_EXPR` is NOT defined), traits are ignored and C++11 rules
(`is_constructible<T, Args..., inner_allocator_type>::value` and
`is_constructible<T, allocator_arg_t, inner_allocator_type, Args...>::value`)
will be used to detect if the allocator must be propagated with suffix or prefix allocator arguments.

[endsect]

[section:insertion_hints Insertion hints in associative containers and preserving
 insertion ordering for elements with equivalent keys]

[@http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#233 LWG Issue #233] corrected a defect
in C++98 and specified how equivalent keys were to be inserted in associative containers. [*Boost.Container]
implements the C++11 changes that were specified in [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1780.html N1780
['Comments on LWG issue 233: Insertion hints in associative containers]]:

* `a_eq.insert(t)`: If a range containing elements equivalent to t exists in a_eq, t is inserted at the end of that range.
* `a_eq.insert(p,t)`: t is inserted as close as possible to the position just prior to p.

[endsect]

[section:initializer_lists Initializer lists]

[*Boost.Container] supports initialization, assignments and insertions from initializer lists
in compilers that implement this feature.

[endsect]

[section:null_iterators Null Forward Iterators]

[*Boost.Container] implements
[@http://www.open-std.org/JTC1/sc22/WG21/docs/papers/2013/n3644.pdf C++14 Null Forward Iterators],
which means that value-initialized iterators may be compared and compare equal
to other value-initialized iterators of the same type. Value initialized iterators behave as if they refer
past the end of the same empty sequence (example taken from N3644):

[c++]

   vector<int> v = { ... };
   auto ni = vector<int>::iterator();
   auto nd = vector<double>::iterator();
   ni == ni; // True.
   nd != nd; // False.
   v.begin() == ni; // ??? (likely false in practice).
   v.end() == ni;   // ??? (likely false in practice).
   ni == nd; // Won't compile.

[endsect]

[section:polymorphic_memory_resources Polymorphic Memory Resources ]

The document
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4480.html C++ Extensions for Library Fundamentals (final draft)]
includes classes that provide allocator type erasure and runtime polymorphism. As Pablo Halpern, the author of the proposal,
explains in the paper ([@https://isocpp.org/files/papers/N3916.pdf N3916 Polymorphic Memory Resources (r2)]):

["['A significant impediment to effective memory management in C++ has been the 
inability to use allocators in non-generic contexts.  In large software systems,
most of  the application program consists of non-generic procedural or
object-oriented code that is compiled once and linked many times.]]

["['Allocators in C++, however, have historically relied solely on
compile-time polymorphism, and therefore have not been suitable for use in vocabulary
types, which are passed through interfaces between separately-compiled modules,
because the allocator type necessarily affects the type of the object that uses it.
This proposal builds upon the improvements made to allocators in 
C++11 and describes a set of facilities for runtime polymorphic memory 
resources that interoperate with the existing compile-time polymorphic 
allocators.]]

Most utilities from the Fundamentals TS were merged into C++17, but
[*Boost.Container] offers them for C++03, C++11 and C++14 compilers.

[*Boost.Container] implements nearly all classes of the proposal under
the namespace `boost::container::pmr`. There are two groups,

*  Header only utilities (these don't require the separately compiled library): 
   *	[classref boost::container::pmr::memory_resource memory_resource].
   *	[classref boost::container::pmr::resource_adaptor resource_adaptor].

*  Utilities that require the the separately compiled library: 
   *	[classref boost::container::pmr::polymorphic_allocator polymorphic_allocator].
   *	[classref boost::container::pmr::monotonic_buffer_resource monotonic_buffer_resource].
   *	[classref boost::container::pmr::unsynchronized_pool_resource unsynchronized_pool_resource].
   *	[classref boost::container::pmr::synchronized_pool_resource synchronized_pool_resource].
   *  Global resource functions: [funcref  boost::container::pmr::get_default_resource get_default_resource]/
      [funcref  boost::container::pmr::set_default_resource set_default_resource]/
      [funcref  boost::container::pmr::new_delete_resource  new_delete_resource]/
      [funcref  boost::container::pmr::null_memory_resource null_memory_resource]
   *  Aliases for boost containers using the polymorphic allocator
      (like [classref boost::container::pmr::vector pmr::vector], etc.)

[*Boost.Container]'s polymorphic resource library is usable from C++03 containers,
and offers some alternative utilities if the required C++11 features of the
['Library Fundamentals] specification are not available.

Finally, [*Boost.Container]'s polymorphic resource library includes support for
dynamic memory allocation for over-aligned types (introduced in C++17), in older
platforms.

[import ../example/doc_pmr.cpp]

Let's review the usage example given in
[@https://isocpp.org/files/papers/N3916.pdf N3916] and see how it can be implemented
using [*Boost.Container]: ['Suppose we are processing a series of shopping lists, where a shopping list is a
container of strings, and storing them in a collection (a list) of shopping lists.
Each shopping list being processed uses a bounded amount of memory that is needed for
a short period of time, while the collection of shopping lists uses an unbounded
amount of memory and will exist for a longer period of time. For efficiency, we can
use a more time-efficient memory allocator based on a finite buffer for the temporary
shopping lists.]

Let's see how `ShoppingList` can be defined to support an polymorphic memory resource
that can allocate memory from different underlying mechanisms. The most important
details are:

* It should declare that supports an allocator defining an `allocator_type` typedef.
  This `allocator_type` will be of type [classref boost::container::pmr::memory_resource memory_resource *],
  which is a base class for polymorphic resources.
* It must define constructors that take the 
  the allocator as argument. It can be implemented in two ways:
   * `ShoppingList` has constructors taking
      [classref boost::container::pmr::memory_resource memory_resource*] as the last argument.
   * `ShoppingList` has constructors taking
      [classref boost::container::allocator_arg_t allocator_arg_t] as the first argument
     and [classref boost::container::pmr::memory_resource memory_resource*] as the second argument.

[*Note:] ['In C++03 compilers, it is required that the programmer specializes as `true`
[classref boost::container::constructible_with_allocator_suffix constructible_with_allocator_suffix] or
[classref boost::container::constructible_with_allocator_prefix constructible_with_allocator_prefix]
as in C++03 there is no way to automatically detect the chosen option at compile time. If
no specialization is done, [*Boost.Container] assumes the suffix option].

[doc_pmr_ShoppingList_hpp]

['However, this time-efficient allocator is not appropriate for the longer
lived collection of shopping lists. This example shows how those temporary shopping
lists, using a time-efficient allocator, can be used to populate the long lived collection
of shopping lists, using a general purpose allocator, something that would be
annoyingly difficult without the polymorphic allocators.]

In [*Boost.Container] for the time-efficient allocation we can use
[classref boost::container::pmr::monotonic_buffer_resource monotonic_buffer_resource],
providing an external buffer that will be used until it's exhausted. In the default
configuration, when the buffer is exhausted, the default memory resource will be used
instead.

[doc_pmr_main_cpp]

['Notice that the shopping lists within `folder` use the default allocator resource
whereas the shopping list `temporaryShoppingList` uses the short-lived but very fast
`buf_rsrc`. Despite using different allocators, you can insert
`temporaryShoppingList` into folder because they have the same `ShoppingList`
type. Also, while `ShoppingList` uses memory_resource directly,
[classref boost::container::pmr::list pmr::list],
[classref boost::container::pmr::vector pmr::vector]
and [classref boost::container::pmr::string pmr::string] all use 
[classref boost::container::pmr::polymorphic_allocator polymorphic_allocator].]

['The resource passed to the `ShoppingList` constructor is propagated to the vector and
each string within that `ShoppingList`. Similarly, the resource used to construct
`folder` is propagated to the constructors of the ShoppingLists that are inserted into
the list (and to the strings within those `ShoppingLists`). The
[classref boost::container::pmr::polymorphic_allocator polymorphic_allocator]
template is designed to be almost interchangeable with a pointer to
[classref boost::container::pmr::memory_resource memory_resource],
thus producing a ['bridge] between the template-policy
style of allocator and the polymorphic-base-class style of allocator.]

This example actually shows how easy is to use [*Boost.Container] to write
type-erasured allocator-capable classes even in C++03 compilers.

[endsect]


[section:forward_list `forward_list<T>`]

[*Boost.Container] does not offer C++11 `forward_list` container yet, but it will be available in future
versions.

[endsect]

[section:vector_exception_guarantees `vector` vs. `std::vector` exception guarantees]

[classref boost::container::vector vector] does not support the strong exception guarantees
given by `std::vector` in functions like `insert`, `push_back`, `emplace`, `emplace_back`,
`resize`, `reserve` or `shrink_to_fit` for either copyable or no-throw moveable classes.
In C++11 [@http://en.cppreference.com/w/cpp/utility/move_if_noexcept move_if_noexcept] is used
to maintain C++03 exception safety guarantees combined with C++11 move semantics.
This strong exception guarantee degrades the insertion performance of copyable and throwing-moveable types,
degrading moves to copies when such types are inserted in the vector using the aforementioned
members.

This strong exception guarantee also precludes the possibility of using some type of
in-place reallocations that can further improve the insertion performance of `vector` See
[link container.extended_allocators Extended Allocators] to know more
about these optimizations.

[classref boost::container::vector vector] always uses move constructors/assignments
to rearrange elements in the vector and uses memory expansion mechanisms if the allocator supports them,
while offering only basic safety guarantees. It trades off exception guarantees for an improved performance.

[endsect]

[section:container_const_reference_parameters Parameter taken by const reference that can be changed]

Several container operations use a parameter taken by const reference that can be changed during execution of the function.
[@http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#526 LWG Issue 526
   (['Is it undefined if a function in the standard changes in parameters?])]
discusses them:

[c++]

   //Given std::vector<int> v
   v.insert(v.begin(), v[2]);
   //v[2] can be changed by moving elements of vector

   //Given std::list<int> l:
   l.remove(*l.begin())
   //The operation could delete the first element, and then continue trying to access it.

The adopted resolution, NAD (Not A Defect), implies that previous operations must be well-defined. This requires code
to detect a reference to an inserted element and an additional copy in that case, impacting performance even when
references to already inserted objects are not used. Note that equivalent functions taking rvalue references or
iterator ranges require elements not already inserted in the container.

[*Boost.Container] prioritizes performance and has not implemented the NAD resolution:
in functions that might modify the argument, the library requires references to elements not stored
in the container. Using references to inserted elements yields to undefined behaviour (although in debug mode, this
precondition violation could be notified via BOOST_ASSERT).

[endsect]

[section:Vector_bool `vector<bool>` specialization]

`vector<bool>` specialization has been quite problematic, and there have been several
unsuccessful tries to deprecate or remove it from the standard. [*Boost.Container] does not implement it
as there is a superior [@http://www.boost.org/libs/dynamic_bitset/ Boost.DynamicBitset]
solution. For issues with `vector<bool>` see the following papers:

* [@http://howardhinnant.github.io/onvectorbool.html On `vector<bool>`]
* [@http://www.gotw.ca/publications/N1211.pdf vector<bool>: N1211: More Problems, Better Solutions],
* [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2160.html N2160: Library Issue 96: Fixing vector<bool>],
* [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2204.html N2204 A Specification to deprecate vector<bool>].

Quotes:

* ["['But it is a shame that the C++ committee gave this excellent data structure the name vector<bool> and
  that it gives no guidance nor encouragement on the critical generic algorithms that need to be optimized for this
  data structure. Consequently, few std::lib implementations go to this trouble.]]

* ["['In 1998, admitting that the committee made a mistake was controversial.
  Since then Java has had to deprecate such significant portions of their libraries
  that the idea C++ would be ridiculed for deprecating a single minor template specialization seems quaint.]]

* ["['`vector<bool>` is not a container and `vector<bool>::iterator` is not a random-access iterator
(or even a forward or bidirectional iterator either, for that matter). This has already broken user code
in the field in mysterious ways.]]

* ["['`vector<bool>` forces a specific (and potentially bad) optimization choice on all users by enshrining
it in the standard. The optimization is premature; different users have different requirements. This too
has already hurt users who have been forced to implement workarounds to disable the 'optimization'
(e.g., by using a vector<char> and manually casting to/from bool).]]

So `boost::container::vector<bool>::iterator` returns real `bool` references and works as a fully compliant container.
If you need a memory optimized version of `boost::container::vector<bool>`, please use
[@http://www.boost.org/libs/dynamic_bitset/ Boost.DynamicBitset].

[endsect]

[section:non_standard_memset_initialization Non-standard value initialization using `std::memset`]

[*Boost.Container] uses `std::memset` with a zero value to initialize some types as in most platforms this
initialization yields to the desired value initialization with improved performance.

Following the C11 standard, [*Boost.Container] assumes that ['for any integer type,
the object representation where all the bits are zero shall be a representation of the value
zero in that type]. Since `_Bool`/`wchar_t`/`char16_t`/`char32_t` are also integer types in C, it considers
all C++ integral types as initializable via `std::memset`.

By default, [*Boost.Container] also considers floating point types to be initializable using `std::memset`.
Most platforms are compatible with this initialization, but in case this initialization is not desirable the
user can `#define BOOST_CONTAINER_MEMZEROED_FLOATING_POINT_IS_NOT_ZERO` before including library headers.

By default, it also considers pointer types (pointer and pointer to function types, excluding
member object and member function pointers) to be initializable using `std::memset`.
Most platforms are compatible with this initialization, but in case this initialization is not desired the
user can `#define BOOST_CONTAINER_MEMZEROED_POINTER_IS_NOT_ZERO` before including library headers.

[endsect]

[endsect]

[section:some_comparisons Boost container attributes and comparison with standard library implementations]

[section:sizeof `sizeof` comparison across major implementations]

These two tables compare `sizeof(container)` across major implementations and Boost.Container.

[table:sizeof_comparison sizeof comparison in 32/64 bit systems
[[Container]      [Boost.Container ]  [libstdc++ (GCC)] [libc++ (Clang)] [Microsoft STL [footnote Uses heap-allocated sentinels for `list` and `[multi_]set/map`, resulting in a smaller `sizeof` but requiring allocation on construction.]]]
[[`vector`]         [12 / 24]         [12 / 24]         [12 / 24]        [12 / 24]  ]
[[`deque`]          [16 / 32]         [40 / 80]         [24 / 48]        [20 / 40]  ]
[[`list`]           [12 / 24]         [12 / 24]         [12 / 24]        [8 / 16]   ]
[[`multi_set/map`]  [16 / 32]         [24 / 48]         [12 / 24]        [8 / 16]   ]
[[`string` [footnote Boost.Container has a SSO size option
                  ([classref boost::container::inline_chars inline_chars]) that changes the `sizeof`.
                   The number shown is the `sizeof` for the default SSO size]]
                    [12 / 24]         [24 / 32]         [12 / 24]        [24 / 32]  ]
]

[endsect]

[section:string_sso String Small String Optimization (SSO) comparison across major implementation]

This tables shows the number of characters (excluding the null terminator) that can be hold inline across major implementations and Boost.Container.

[table:sso_capacity SSO capacity for string
[[Mode]     [Boost.Container [footnote Boost.Container has a SSO size selection (up to 127 characters) option called [classref boost::container::inline_chars inline_chars] ]]
                             [libstdc++ (GCC)] [libc++ (Clang)] [Microsoft STL]]
[[32 bit]   [10]              [15]         [10]        [15]]
[[64 bit]   [22]              [15]         [22]        [15]]
]

[endsect]

[section:deque_blocks `deque` implementation block/segment size comparison]

`deque` implementations are based on a segmented array of blocks, and the block size is an important parameter that affects performance.
This table shows the block size in bytes for `deque` implementations across major implementations and Boost.Container.

[table:block_sizes Deque Block Sizes
[[Implementation]   [Block Size in bytes]                   ]
[[Boost.Container]  [512 (32-bit) / 1024 (64-bit) [footnote [classref boost::container::deque deque] & [classref boost::container::segtor segtor] have an option to select the [classref boost::container::block_size block_size] ] ] ]
[[libstdc++ (GCC)]  [512 ]                                  ]
[[libc++ (Clang)]   [4096]                                  ]
[[Microsoft STL]    [16]                                    ]
]

[endsect]

[section:boost_sizeof `sizeof` value of Boost.Container containers]

[table:sizeof_comparison `sizeof` comparison between Boost Containers (in bytes)

This table shows the `sizeof` value of Boost.Container containers in 32 and 64 bit systems. Note that these values can be changed by configuration options
(like [classref boost::container::stored_size stored_size]) so they are shown here for the default configuration.

[[Container]         [32-bit] [64-bit] ]
[[`vector`]            [12]     [24] ]
[[`deque`]             [16]     [32] ]
[[`devector`]          [16]     [32] ]
[[`segtor`]  [12]     [24] ]
[[`stable_vector`]     [20]     [40] ]
[[`list`]              [12]     [24] ]
[[`slist`]             [8]      [16] ]
[[`map/set`]           [16]     [32] ]
[[`flat_[multi_]map/set` [footnote `boost::containter::flat_xxx` containers are by default ordered `vector`s, but these containers can be configure to use another container as the underlying sequence ] ]
                       [12]     [24] ]
[[`string`]            [12]     [24] ]
]

[endsect]

[endsect]

[import ../../../tools/auto_index/include/auto_index_helpers.qbk]

[section:index_reference Indexes and Reference]

[section:index Indexes]

[named_index class_name Class Index]
[named_index typedef_name Typedef Index]
[named_index function_name Function Index]
[/named_index macro_name Macro Index]
[/index]

[endsect]

[xinclude autodoc.xml]

[endsect]

[section:ack_notes History, acknowledgements and Release Notes]

[section:boost_container_history Boost.Container history]

[*Boost.Container] is a product of a long development effort that started
[@http://lists.boost.org/Archives/boost/2004/11/76263.php in 2004 with the experimental Shmem library],
which pioneered the use of standard containers in shared memory. Shmem included modified SGI STL container
code tweaked to support non-raw `allocator::pointer` types and stateful allocators. Once reviewed,
Shmem was accepted as [@http://www.boost.org/libs/interprocess/ Boost.Interprocess] and this library
continued to refine and improve those containers.

In 2007, container code from node containers (`map`, `list`, `slist`) was rewritten, refactored
and expanded to build the intrusive container library [@http://www.boost.org/libs/intrusive/ Boost.Intrusive].
[*Boost.Interprocess] containers were refactored to take advantage of [*Boost.Intrusive] containers and
code duplication was minimized. Both libraries continued to gain support and bug fixes for years.
They introduced move semantics, emplacement insertion and more features of then unreleased C++0x
standard.

[*Boost.Interprocess] containers were always standard compliant, and those containers and new
containers like `stable_vector` and `flat_[multi]set/map` were used outside [*Boost.Interprocess]
with success. As containers were mature enough to get their own library, it was a natural step to
collect them containers and build [*Boost.Container], a library targeted to a wider audience.

[endsect]

[section:acknowledgements_notes Acknowledgements, notes and links]

*  Original standard container code comes from [@http://www.sgi.com/tech/stl/ SGI STL library],
   which enhanced the original HP STL code. Code was rewritten for
   [*Boost.Interprocess] and moved to [*Boost.Intrusive]. Many thanks to Alexander Stepanov, Meng Lee, David Musser,
   Matt Austern... and all HP and SGI STL developers.

*  `flat_[multi]_map/set` containers were originally based on [@http://en.wikipedia.org/wiki/Loki_%28C%2B%2B%29 Loki's]
   AssocVector class. Code was rewritten and expanded for [*Boost.Interprocess], so thanks to Andrei Alexandrescu.

*  `stable_vector` was invented and coded by
   [@http://bannalia.blogspot.com/2008/09/introducing-stablevector.html Joaqu\u00EDn M. L\u00F3pez Mu\u00F1oz],
   then adapted for [*Boost.Interprocess]. Thanks for such a great container.

*  `static_vector` was based on Andrew Hundt's and Adam Wulkiewicz's high-performance `varray` class.
   Many performance improvements of `vector` were also inspired by their implementation. Thanks!

*  `devector`'s initial implementation is based on Thaler Benedek's high-performance `devector` implementation,
   then adapted for [*Boost.Container]. Also inspired by similar implemenations by Orson Peters and Lars Hagen.
   Thanks for such a great code and documentation!

*  Howard Hinnant's help and advices were essential when implementing move semantics,
   improving allocator support or implementing small string optimization. Thanks Howard
   for your wonderful standard library implementations.

*  And finally thanks to all Boosters who helped all these years, improving, fixing and
   reviewing all my libraries.

[endsect]

[section:release_notes Release Notes]

[section:release_notes_boost_1_91_00 Boost 1.91 Release]

* Implemented heterogeneous overloads from C++23 ([@http://wg21.link/p2077r3 P2077]) and C++26 ([@http://wg21.link/P2363 P2363]).
* In C++20 compilers, `static_vector<T>`'s destructor is now trivial if `T` is trivial.
* Uses-allocator construction now handles prefix and suffix allocator conventions even in C++03.
* Implemented C++20's [funcref boost::container::uninitialized_construct_using_allocator uninitialized_construct_using_allocator]
  and [funcref boost::container::make_obj_using_allocator make_obj_using_allocator].
* Added `[[nodiscard]]` to several allocator and PMR utilities.
* Implemented overaligned allocation support for `new_allocator` and `pmr::new_delete_resource()`:
   * If available, uses C++17's utilities under the `__cpp_aligned_new` feature.
   * Uses alternative aligned allocation functions (`posix_memalign`, `aligned_alloc`, `_aligned_malloc`...) otherwise.
* Implemented overaligned allocation support for `adaptive_pool`and `node_allocator`
* Changed return type of `erase`/`erase_if`/`unique` members of `list` and `slist` to `size_type` to follow C++20 changes to `std::list`.
* Updated `basic_string`:
   * Added missing `string_view` members and updated `operator[]` to be able to return the terminating null.
   * Added C++20 `starts_with`/`ends_with` and C++23 `contains` overloads.
   * Added null pointer checks for `basic_string` methods taking `const CharT*` parameters.
   * Deleted constructor from `std::nullptr_t`.
   * Added [classref boost::container::inline_chars inline_chars],
     [classref boost::container::growth_factor growth_factor] and
     [classref boost::container::stored_size stored_size] options to [classref boost::container::basic_string basic_string].
   * New [classref boost::container::segtor segtor] container: the single ended brother of
     [classref boost::container::deque deque]: a random-access sequence container with segmented
      (block-based) storage like deque but only growth at the back.
* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/323 GitHub #323: ['"flat_tree::try_emplace UB"]].
   * [@https://github.com/boostorg/container/issues/328 GitHub #328: ['"boost::container::deque stores a redundant copy of the allocator, increasing size"]].
   * [@https://github.com/boostorg/container/issues/332 GitHub #332: ['"aligned_alloc not available in C++11/14 on XCode 12"]].

[endsect]

[section:release_notes_boost_1_90_00 Boost 1.90 Release]

* Reimplemented [classref boost::container::deque]. The original implementation was based on
   the SGI's original data structure (similar to libstdc++). Main changes:
   * `sizeof(deque)` was 10 words, now is 4 words. Probably the lightest implementation around.
   * `sizeof(deque::iterator)` was 4 words, now is is 2 words (similar to libc++ and MSVC).
   * Several internal algorithms were reimplemented to speed up the segmented nature of deque.
   * Defaults were slightly changed, 64 bit platforms now use 1024 byte blocks by default
     instead of classic SGI 512 byte blocks.
   * The new implementation eases further deque-like variations and optimizations in the future.

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/248 GitHub #248: ['"flat_map slow insertion introduced in boost-1.80.0"]].
   * [@https://github.com/boostorg/container/issues/254 GitHub #254: ['"C++20 std::erase_if"]].
   * [@https://github.com/boostorg/container/issues/293/ GitHub #293: ['"UBSAN reports unaligned access error"]].
   * [@https://github.com/boostorg/container/pull/294 GitHub #294: ['"CMake: Add option to use header-only Boost::container"]].
   * [@https://github.com/boostorg/container/issues/300 GitHub #300: ['"Warnings when building with clang-20"]].
   * [@https://github.com/boostorg/container/issues/304 GitHub #304: ['"Usage of boost::container::small_vector with custom allocator"]].
   * [@https://github.com/boostorg/container/pull/305 GitHub #305: ['"Warnings with -Wstrict-prototypes"]].
   * [@https://github.com/boostorg/container/pull/307 GitHub #307: ['"Fix all instances of MSVC warning C4146 (unsigned negation)"]].
   * [@https://github.com/boostorg/container/issues/309 GitHub #309: ['"Performance regression of boost::container::static_vector introduced in boost v1.86"]].
   * [@https://github.com/boostorg/container/issues/306 GitHub #306: ['"new_allocator.hpp error: '__cpp_sized_deallocation' is not defined, evaluates to 0 [-Werror,-Wundef]"]].
   * [@https://github.com/boostorg/container/issues/310 GitHub #310: ['"flat_map: Mention correct type in documentation of emplace and emplace_hint"]].
   * [@https://github.com/boostorg/container/issues/312 GitHub #312: ['"flat_map std::allocator::is_always_equal is deprecated"]].
   * [@https://github.com/boostorg/container/pull/317/ GitHub #317: ['"Partial revert of changes for Issue #209 - compiler warnings"]].
   * [@https://github.com/boostorg/container/pull/321/ GitHub #321: ['"devector does not work with pmr allocators"]].

[endsect]

[section:release_notes_boost_1_89_00 Boost 1.89 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/250 GitHub #250: ['"Custom container leads to invalid use of incomplete type for struct boost::container::dtl::container_rebind"]].

[endsect]

[section:release_notes_boost_1_88_00 Boost 1.88 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/297 GitHub #297: ['"flat_map::try_emplace does not compile if allocator has construct"]].
   * [@https://github.com/boostorg/container/issues/234 GitHub #234: ['"dlmalloc_ext_2_8_6.c:warning: iteration 2305843009213693951 invokes undefined behavior"]].

[endsect]

[section:release_notes_boost_1_87_00 Boost 1.87 Release]

* Added [classref boost::container::stored_size stored_size] option to
  [classref boost::container::static_vector static_vector] and
  [classref boost::container::small_vector small_vector].

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/261 GitHub #261: ['"End iterators are not dereferencable"]].
   * [@https://github.com/boostorg/container/issues/288 GitHub #288: ['"Compile error when using flat_map::extract_sequence with small_vector"]].
   * [@https://github.com/boostorg/container/issues/295 GitHub #295: ['"Bug in small_vector::swap"]].
   * [@https://github.com/boostorg/container/issues/296 GitHub #296: ['"flat_{set,map} does illegal things when confronted with duplicate values in initialization"]].

[endsect]

[section:release_notes_boost_1_86_00 Boost 1.86 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/241 GitHub #241: ['"flat_map should support same interface as std::map"]].
   * [@https://github.com/boostorg/container/issues/245 GitHub #245: ['"flat_tree::insert ordered range doesn't assert sorting"]].
   * [@https://github.com/boostorg/container/issues/259 GitHub #259: ['"Global variables"]].
   * [@https://github.com/boostorg/container/issues/266 GitHub #266: ['"small_vector<T> is misaligned on the stack in 32 bits"]].
   * [@https://github.com/boostorg/container/issues/269 GitHub #269: ['"flat_multimap::emplace not sorting elements under GCC"]].
   * [@https://github.com/boostorg/container/issues/273 GitHub #273: ['"flat_map/vector crashes on appends (memory corruption)"]].
   * [@https://github.com/boostorg/container/issues/275 GitHub #275: ['"Compilation fails if custom key comparison is used"]].
   * [@https://github.com/boostorg/container/issues/277 GitHub #277: ['"Remove dep on boost::static_assert"]].
   * [@https://github.com/boostorg/container/issues/279 GitHub #279: ['"small_vector cannot go back to use stack space"]].
   * [@https://github.com/boostorg/container/issues/280 GitHub #280: ['"Several containers don't support non-movable types when move assigning"]].
   * [@https://github.com/boostorg/container/issues/285 GitHub #285: ['"devector<>::push_front asserts after clear()"]].

[endsect]

[section:release_notes_boost_1_85_00 Boost 1.85 Release]

* Removed Boost.StaticAssert dependency.

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/225 GitHub #225: ['"variable set but not used in dlmalloc_ext_2_8_6.c"]].
   * [@https://github.com/boostorg/container/issues/242 GitHub #242: ['"Issue with string::rfind"]].

[endsect]

[section:release_notes_boost_1_83_00 Boost 1.83 Release]

* Disabled forceinline for Clang due to code bloat issues, see [@https://lists.boost.org/boost-users/2023/04/91445.php Boost mailing list report]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/225 GitHub #225: ['"variable set but not used in dlmalloc_ext_2_8_6.c"]].
   * [@https://github.com/boostorg/container/issues/242 GitHub #242: ['"Issue with string::rfind"]].

[endsect]

[section:release_notes_boost_1_82_00 Boost 1.82 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/232 GitHub #232: ['"Fix using pmr::polymorphic_allocator in pre-main"]].
   * [@https://github.com/boostorg/container/issues/233 GitHub #233: ['"Can't std::move small_vector with move-only type"]].
   * [@https://github.com/boostorg/container/issues/238 GitHub #238: ['"Containers should not be using memset to value-initialize POD types"]].
   * [@https://github.com/boostorg/container/issues/236 GitHub #236: ['"flat_tree::erase_unique uses wrong iterator"]].
   * [@https://github.com/boostorg/container/issues/240 GitHub #240: ['"_GLIBCXX_DEBUG detects issues in flat_set/map"]].

[endsect]

[section:release_notes_boost_1_81_00 Boost 1.81 Release]

* [classref boost::container::devector devector]'s insertion logic has been reimplemented to move elements to the center of the devector if an insertion at one end
  has no free capacity but there is free capacity on the other end. Current implementation keeps reallocating memory when only inserting at one end and poping from the
  other, provoking very high memory usage. The new strategy is based on the article
  [@http://larshagencpp.github.io/blog/2016/05/22/devector Double-ended vector - is it useful?] by Lars Greger Nordland Hagen.

[endsect]

[section:release_notes_boost_1_80_00 Boost 1.80 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/209 GitHub #209: ['"Some boost warnings with my R package (Wclass-memaccess warnings with std::pair)"]].
   * [@https://github.com/boostorg/container/issues/211 GitHub #211: ['"Use atomics for pmr get/set default resource"]].
   * [@https://github.com/boostorg/container/issues/210 GitHub #210: ['"Use sized delete in boost::container::new_allocator if __cpp_sized_deallocation is defined"]].
   * [@https://github.com/boostorg/container/issues/218 GitHub #218: ['"small_vector static capacity is too small when not a multiple of 8 bytes"]].
   * [@https://github.com/boostorg/container/issues/221 GitHub #221: ['"flat_set and friends should offer a const sequence_type& sequence() const method (...)"]].
   * [@https://github.com/boostorg/container/pull/222   GitHub #222: ['"Fix incomplete type error when using list with pair"]].
   * [@https://github.com/boostorg/container/issues/223 GitHub #223: ['"Possible copypaste typo"]].

[endsect]

[section:release_notes_boost_1_79_00 Boost 1.79 Release]

* The library now compiles without warnings with GCC's -Wcast-align=strict
* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/195    GitHub #195: ['"vec_iterator member typedef iterator_concept should only be defined in C++20"]].
   * [@https://github.com/boostorg/container/issues/199    GitHub #199: ['"Apply LWG issue 3471 to memory_resource"]].
   * [@https://github.com/boostorg/container/issues/204    GitHub #204: ['"Inconsistent noexcept-ness of static_vector::reserve"]].
   * [@https://github.com/boostorg/container/issues/206    GitHub #206: ['"operator-> on static_vector::iterator causes cast alignment warning"]].
   * [@https://github.com/boostorg/container/issues/207    GitHub #207: ['"boost.vector doesn't work with common_iterator"]].
   * [@https://github.com/boostorg/container/issues/214    GitHub #214: ['"string is not properly null-terminated in assignments"]].

[endsect]

[section:release_notes_boost_1_78_00 Boost 1.78 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/186    GitHub #186: ['"Warnings out the wazoo"]].
   * [@https://github.com/boostorg/container/issues/187    GitHub #187: ['"flat_map::erase and unique keys"]].
   * [@https://github.com/boostorg/container/issues/188    GitHub #188: ['"Build fails when RTTI is disabled"]].
   * [@https://github.com/boostorg/container/issues/192    GitHub #192: ['"basic_string::clear() has poor codegen compared to STL implementations"]].
   * [@https://github.com/boostorg/container/issues/197    GitHub #197: ['"small_vector::swap causes spurious allocations and suboptimal performance"]].

[endsect]

[section:release_notes_boost_1_77_00 Boost 1.77 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/150    GitHub #150: ['"Use std::contiguous_iterator_tag if available"]].
   * [@https://github.com/boostorg/container/issues/180    GitHub #180: ['"polymorphic_allocator's copy special member functions are not noexcept"]].
   * [@https://github.com/boostorg/container/issues/184    GitHub #184: ['"Issues with custom exceptions implementation"]].
   * [@https://github.com/boostorg/container/issues/185    GitHub #185: ['"Including headers adds exports"]].

[endsect]

[section:release_notes_boost_1_76_00 Boost 1.76 Release]

* Added [[no-discard]] attribute in all containers to catch bugs related to unused return values.

* Replaced default standard exception classes with Boost.Container own classes, reducing considerably the included files overhead.
  Example: in MSVC 19 `boost/container/vector.hpp` preprocessed file size reduces from 1,5MB to 930KB. If you still want to use
  standard exception classes, you can define `BOOST_CONTAINER_USE_STD_EXCEPTIONS` before using any Boost.Container class.

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/102    GitHub #102: ['"flat_map::insert ambiguous with initializer list & pairs that need to convert"]].
   * [@https://github.com/boostorg/container/issues/139    GitHub #139: ['"flat_map merge and iterators"]].
   * [@https://github.com/boostorg/container/issues/141    GitHub #141: ['"small_vector does not propagate no throw properties of move operation of contained type"]].
   * [@https://github.com/boostorg/container/issues/164    GitHub #164: ['"Compile error when using `pmr::map` with a `std::pair`; works when using a `std::tuple`"]].
   * [@https://github.com/boostorg/container/issues/171    GitHub #171: ['"deque::clear() uses undefined behaviour"]].

[endsect]

[section:release_notes_boost_1_75_00 Boost 1.75 Release]

* New [classref boost::container::devector devector] container.

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/152    GitHub #152: ['"Tree-based containers have troubles with move-only types"]].
   * [@https://github.com/boostorg/container/issues/156    GitHub #156: ['"Compile error with vector"]].
   * [@https://github.com/boostorg/container/pull/157      GitHub #157: ['"Add missing include"]].
   * [@https://github.com/boostorg/container/issues/159    GitHub #159: ['"pmr::monotonic_buffer_resource crashes on large single allocations"]].
   * [@https://github.com/boostorg/container/issues/160    GitHub #160: ['"Usage of uses_allocator needs a remove_cvref_t"]].
   * [@https://github.com/boostorg/container/issues/162    GitHub #162: ['"small_vector on MSVC x86 call-by-value crash"]].
   * [@https://github.com/boostorg/container/issues/161    GitHub #161: ['"polymorphic_allocator(memory_resource*) non-standard extension causes headache"]].
   * [@https://github.com/boostorg/container/pull/163      GitHub #163: ['"container_rebind for small_vector with options"]].
   * [@https://github.com/boostorg/container/issues/165    GitHub #165: ['"Link error with shared library and memory_resource inline members"]].
   * [@https://github.com/boostorg/container/pull/166      GitHub #166: ['"Fix encoding error in copyright headers"]].
   * [@https://github.com/boostorg/container/pull/167      GitHub #167: ['"error: the address of 'msg' will always evaluate as 'true' warning with GCC 4.4"]].
   * [@https://github.com/boostorg/container/issues/169    GitHub #169: ['"flood of warnings building dlmalloc_ext_2_8_6.c on clang11"]].

[endsect]

[section:release_notes_boost_1_74_00 Boost 1.74 Release]

* Fixed bugs/issues:
   * [@https://github.com/boostorg/container/issues/125    GitHub #125: ['"flat_map doc misleading complexity"]].
   * [@https://github.com/boostorg/container/issues/126    GitHub #126: ['"flat_set.hpp and set.hpp in pmr have the same header guard"]].
   * [@https://github.com/boostorg/container/issues/128    GitHub #128: ['"moved from small_vector and static_vector calls destructor on elements in static part"]].
   * [@https://github.com/boostorg/container/issues/129    GitHub #129: ['"Alias templates for small_flat_[multi]{set|map} using small_vector as container"]].
   * [@https://github.com/boostorg/container/pull/135      GitHub #135: ['"Missing BOOST_NORETURN for user defined functions"]].
   * [@https://github.com/boostorg/container/pull/137      GitHub #137: ['"RandomAccessIterator + 0"]].
   * [@https://github.com/boostorg/container/pull/138      GitHub #138: ['"Remove Classes from Global Namespace"]].
   * [@https://github.com/boostorg/container/issues/142    GitHub #142: ['"memset called with null pointer"]].
   * [@https://github.com/boostorg/container/issues/144    GitHub #144: ['"GCC suggest-override warnings"]].
   * [@https://github.com/boostorg/container/issues/145    GitHub #145: ['"Allocations not handled correctly in some cases of vector move with unequal allocators"]].
   * [@https://github.com/boostorg/container/pull/146      GitHub #146: ['"Changes for Embarcadero C++ clang-based compilers, targeting Boost 1.74. Addition needed for Embarcardero clang-based compilers"]].
   * [@https://github.com/boostorg/container/pull/148      GitHub #148: ['"Fix static initialization issues in pmr global resources"]].
   * [@https://github.com/boostorg/container/pull/149      GitHub #149: ['"InitializeCriticalSectionEx returns "BOOL" (int)"]].
   * [@https://github.com/boostorg/container/issues/151    GitHub #151: ['"Buffer overflow in monotonic_buffer_resource::do_allocate"]].

[endsect]

[section:release_notes_boost_1_72_00 Boost 1.72 Release]

* Fixed bugs:
   * [@https://github.com/boostorg/container/issues/127    GitHub #127: ['"Fix docs for static_vector::max_size() and capacity()"]].
   * [@https://github.com/boostorg/container/issues/132    GitHub #132: ['"flat_map::lower_bound and upper_bound have wrong/misleading docs"]].
   * [@https://github.com/boostorg/container/issues/133    GitHub #133: ['"basic_string move constructor with allocator argument has incorrect allocator check"]].

[endsect]

[section:release_notes_boost_1_71_00 Boost 1.71 Release]

* Fixed bugs:
   * [@https://github.com/boostorg/container/pull/47    GitHub #47: ['"added alignment specification for small_vector"]].
   * [@https://github.com/boostorg/container/issues/88  GitHub #88: ['"Implement C++17 MoveAssignable requirements for self-move assignments"]].
   * [@https://github.com/boostorg/container/issues/107 GitHub #107: ['"Alignment ignored in resource_adaptor"]].
   * [@https://github.com/boostorg/container/pull/109   GitHub #109: ['"Get rid of integer overflow in copy_move_algo.hpp (-fsanitize=integer)"]].
   * [@https://github.com/boostorg/container/pull/110   GitHub #110: ['"Avoid gcc 9 deprecated copy warnings in new_allocator.hpp"]].
   * [@https://github.com/boostorg/container/issues/112 GitHub #112: ['"vector::resize() compilation error with msvc-10..12: data is not a member of boost::detail::aligned_storage"]].
   * [@https://github.com/boostorg/container/issues/114 GitHub #114: ['"Fix small_vector noexcept specification"]].
   * [@https://github.com/boostorg/container/issues/116 GitHub #116: ['"MSVC + boost 1.70 compilation error when windows.h is already included (detail/thread_mutex.hpp)"]].
   * [@https://github.com/boostorg/container/issues/117 GitHub #117: ['"flat_map/map::insert_or_assign with hint has wrong return types"]].
   * [@https://github.com/boostorg/container/issues/118 GitHub #118: ['"Non-unique inplace_set_difference used in in flat_tree_merge_unique and iterator invalidation in insert_unique"]].
   * [@https://github.com/boostorg/container/issues/122 GitHub #122: ['"Fix has_trivial_destructor_after_move"]].
   * [@https://github.com/boostorg/container/issues/123 GitHub #123: ['"With heterogeneous lookup, `equal_range` can result in a range with length greater than 1"]].

* [classref boost::container::deque deque] can now have options, using [classref boost::container::deque_options deque_options].
  The block size/bytes can be be specified.

* [classref boost::container::static_vector static_vector] can now have options, using [classref boost::container::static_vector_options static_vector_options].
    Alignment and throwing behaviour can be be specified.

* [classref boost::container::small_vector small_vector] can now have options, using [classref boost::container::small_vector_options small_vector_options].
    Alignment and growth factor can be be specified.

[endsect]

[section:release_notes_boost_1_70_00 Boost 1.70 Release]

* Removed support for already deprecated GCC < 4.3 and MSVC < 9.0 (Visual 2008) compilers.
* Default allocator parameter changed form `new_allocator<T>` to `void` to reduce symbol lenghts.
* Fixed bugs:
   * [@https://github.com/boostorg/container/pull/96 GitHub #96: ['"Workaround: Intel compilers do not offer CTAD yet"]].
   * [@https://github.com/boostorg/container/issues/97 GitHub #97: ['"buffer overflow in boost::container::flat_map on FreeBSD"]].
   * [@https://github.com/boostorg/container/issues/98 GitHub #98: ['"flat_map: insert_or_assign does not work with hint"]].
   * [@https://github.com/boostorg/container/issues/100 GitHub #100: ['"Compile error on Green Hills: container_detail::flat_tree has no member insert"]].
   * [@https://github.com/boostorg/container/pull/103 GitHub #103: ['"Fix deallocating never-allocated storage in vector.merge()"]].
   * [@https://github.com/boostorg/container/pull/104 GitHub #104: ['"Fix -Wmissing-noreturn clang warnings"]].
   * [@https://github.com/boostorg/container/pull/105 GitHub #105: ['"Fix gcc -Wdeprecated-copy"]].
   * [@https://github.com/boostorg/container/issues/111 GitHub #111: ['"container::vector of interprocess::offset_ptrs to variants holding incomplete type"]].

[endsect]

[section:release_notes_boost_1_69_00 Boost 1.69 Release]

* Deprecated GCC < 4.3 and MSVC < 9.0 (Visual 2008) compilers.

* Implemented C++20 `contains()` for associative containers as specified in
   [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0458r2.html
   P0458R2: Checking for Existence of an Element in Associative Containers].

* Fixed serious bug in heterogeneous lookup functions (is_transparent was broken).

* Fixed bugs:
   * [@https://github.com/boostorg/container/issues/77 GitHub #77: ['"warning: 'sbrk' is deprecated"]].
   * [@https://github.com/boostorg/container/issues/79 GitHub #79: ['"Mark small_vector move operations noexcept"]].
   * [@https://github.com/boostorg/container/issues/80 GitHub #80: ['"flat_map deduction guides are ambiguous"]].
   * [@https://github.com/boostorg/container/issues/81 GitHub #81: ['"Vector with custom allocator does not support value types with operator&"]].
   * [@https://github.com/boostorg/container/issues/82 GitHub #82: ['"Function definition in header file"]].
   * [@https://github.com/boostorg/container/issues/83 GitHub #83: ['"Iterator zero incrementing leads to assert on empty vector"]].
   * [@https://github.com/boostorg/container/pull/84   GitHub #84: ['"Allow vector to be assigned to itself"]].
   * [@https://github.com/boostorg/container/pull/85   GitHub #85: ['"container: misc-typos"]].
   * [@https://github.com/boostorg/container/pull/86   GitHub #86: ['"Add missing warning re-enabling include"]].
   * [@https://github.com/boostorg/container/issues/89 GitHub #89: ['"UBSAN failures detected in preflight CI PR"]].
   * [@https://github.com/boostorg/container/issues/90 GitHub #90: ['"Build fails on clang-5 with libstdc++7-dev (C++17 issue)"]].
   * [@https://github.com/boostorg/container/issues/93 GitHub #93: ['"vector::erase memory leak"]].

[endsect]

[section:release_notes_boost_1_68_00 Boost 1.68 Release]

* Improved correctness of [classref boost::container::adaptive_pool adaptive_pool] and many parameters are now compile-time
  constants instead of runtime constants.

* Implemented C++14's heterogeneous lookup functions for `[multi]map/[multi]set/flat_[multi]map/flat_[multi]set`.

* Added [@https://github.com/boostorg/container/pull/71 GitHub #71: ['"Constructor Template Auto Deduction guides "]].

* Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/13533 Trac #13533:  ['"Boost vector resize causes assert(false)"]].
   * [@https://github.com/boostorg/container/issues/73 GitHub #73: ['"triviality of pair"]].
   * [@https://github.com/boostorg/container/issues/74 GitHub #74: ['"vector assignment not using memcpy"]].
   * [@https://github.com/boostorg/container/issues/75 GitHub #75: ['"flat_set: Heap overflow"]].
   * [@https://github.com/boostorg/container/issues/76 GitHub #76: ['"flat_set: undefined behaviour on empty range"]].
   * Fixed race condition bug in [classref boost::container::pmr::unsynchronized_pool_resource unsynchronized_pool_resource]
     found by Arthur O'Dowyer in his blog post
     [@https://quuxplusone.github.io/blog/2018/06/05/libcpp-memory-resource/ <memory_resource> for libc++]

* Implemented proposed resolution for 
  [@https://cplusplus.github.io/LWG/issue3120 ['"LWG 3120 Unclear behavior of monotonic_buffer_resource::release()"]].
  After `release()` the original buffer is recovered for the next allocation.

[endsect]

[section:release_notes_boost_1_67_00 Boost 1.67 Release]

* ['vector] can now have options, using [classref boost::container::vector_options vector_options].
  The growth factor and the stored size type can be specified.

* Improved range insertion in ['flat_[multi]map/set] containers overall complexity is reduced to O(NlogN).

* Fixed bugs:
   * [@https://github.com/boostorg/container/pull/61 GitHub #61: ['"Compile problems on Android ndk r16 beta 1"]].
   * [@https://github.com/boostorg/container/pull/64 GitHub #64: ['"Fix splice for slist"]].
   * [@https://github.com/boostorg/container/issues/58 GitHub #65: ['"`pmr::monotonic_buffer_resource::allocate()` can return a pointer to freed memory after `release()` is called"]].
   * [@https://svn.boost.org/trac/boost/ticket/13500 Trac #13500:  ['"Memory leak when using erase on string vectors"]].

[endsect]

[section:release_notes_boost_1_66_00 Boost 1.66 Release]

* ['flat_[multi]map/set] can now work as container adaptors, as proposed in [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0429r1.pdf P0429R1].
  The allocator argument is checked for ['size()] and ['empty()] members. If so, the argument is interpreted as the required underlying container.
  This means that ['static_vector], ['stable_vector] and ['small_vector] can be used now with flat associative containers.

* Fixed bugs:
   * [@https://github.com/boostorg/container/pull/54 GitHub #54: ['"no sbrk() in VxWorks, configure dlmalloc to use only mmap"]].
   * [@https://github.com/boostorg/container/issues/58 GitHub #58: ['"Comparing strings does not compile in gcc 7+ in C++17 mode"]].
   * [@https://github.com/boostorg/container/issues/59 GitHub #59: ['"basic_string::npos is missing its definition"]].

[endsect]

[section:release_notes_boost_1_65_00 Boost 1.65 Release]

* Implemented `extract_sequence`, `adopt_sequence` functions for flat_[multi]map/set associative containers.

* Fixed bugs:
   * [@https://github.com/boostorg/container/pull/48 GitHub #48: ['"Replace deprecated/removed C++98 binders"]].
   * [@https://github.com/boostorg/container/pull/49 GitHub #49: ['"Remove useless allocator copy in map"]].
   * [@https://github.com/boostorg/container/pull/50 GitHub #50: ['"Fixed bug Trac #13038 (base64 iterators can't be used with iterator_advance)"]].
   * [@https://github.com/boostorg/container/pull/51 GitHub #51: ['"Fix integer rollover that triggers clang ubsan when U is unsigned"]].

[endsect]

[section:release_notes_boost_1_64_00 Boost 1.64 Release]

* Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/11333 Trac #11333: ['"boost::basic_string_ref should interop with boost::container::basic_string"]].
   * [@https://svn.boost.org/trac/boost/ticket/12749 Trac #12749: ['"container::pmr::polymorphic_allocator compilation error"]].
   * [@https://svn.boost.org/trac/boost/ticket/12915 Trac #12915: ['"Buffer overflow in boost::container::vector (affects flat_set)"]].
   * [@https://github.com/boostorg/container/pull/45 GitHub #45: ['"emplace_back must return reference to back(), not to *end()"]].
   * [@https://github.com/boostorg/container/pull/46 GitHub #46: ['"Fix use of propagate_on_container_swap"]].

[endsect]

[section:release_notes_boost_1_63_00 Boost 1.63 Release]

* Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/12534 Trac #12534: ['"flat_map fails to compile if included after type_traits is instantiated under gcc"]].
   * [@https://svn.boost.org/trac/boost/ticket/12577 Trac #12577: ['"Null reference in pair.hpp triggers runtime warning with -fsanitize=undefined"]].
   * [@https://github.com/boostorg/container/pull/41 GitHub #40: ['Fix parameter types in copy_move_algo.hpp: iterator_traits::difference_type -> allocator_traits::size_type]].
   * [@https://github.com/boostorg/container/pull/41 GitHub #41: ['Avoid -Wunreachable-code in do_allocate()]].

[endsect]

[section:release_notes_boost_1_62_00 Boost 1.62 Release]

* Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/9481  Trac #9481:  ['"Minor comment typo in Boost.Container"]].
   * [@https://svn.boost.org/trac/boost/ticket/9689  Trac #9689:  ['"Add piecewise_construct to boost::container"]].
   * [@https://svn.boost.org/trac/boost/ticket/11170 Trac #11170: ['"Doc slip for index_of"]].
   * [@https://svn.boost.org/trac/boost/ticket/11802 Trac #11802: ['"Incorrect ordering after using insert() with ordered_range_t on a flat_multiset with a non-default sort order"]].
   * [@https://svn.boost.org/trac/boost/ticket/12117 Trac #12117: ['"flat_set constructor with ordered_unique_range"]].
   * [@https://svn.boost.org/trac/boost/ticket/12177 Trac #12177: ['"vector::priv_merge uses unqualified uintptr_t"]].
   * [@https://svn.boost.org/trac/boost/ticket/12183 Trac #12183: ['"GCC 6.1 thinks boost::container::string violates strict aliasing"]].
   * [@https://svn.boost.org/trac/boost/ticket/12256 Trac #12256: ['"set<std::pair<int,int>>::insert cause compilation error in debug configuration in Visual Studio 2012"]].
   * [@https://svn.boost.org/trac/boost/ticket/12273 Trac #12273: ['"static_vector max_size() and capacity() should be constant expressions"]].
     Added constant `static_vector<>::static_capacity` to use the configured capacity in constant expressions.
   * [@https://svn.boost.org/trac/boost/ticket/12286 Trac #12286: ['"PMR flat_map from Boost Container does not compile"]].
   * [@https://svn.boost.org/trac/boost/ticket/12296 Trac #12296: ['"{deque,string} combine for a memory leak"]].
   * [@https://svn.boost.org/trac/boost/ticket/12319 Trac #12319: ['"flat_set` should be nothrow move constructible"]].

* Revised noexcept expressions of default and move constructors in all containers.
* Implemented C++17's `insert_or_assign`/`try_emplace` for [classref boost::container::map map] and [classref boost::container::flat_map flat_map].
* Implemented C++17's [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0083r3.pdf ['Splicing Maps and Sets (Revision 5)]]
   for [classref boost::container::map map], [classref boost::container::multimap multimap],
   [classref boost::container::set set], [classref boost::container::multiset multiset].
* Implemented C++17's [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0084r2.pdf ['P0084R2 Emplace Return Type]]
  in `deque`, `vector`, `stable_vector`, `small_vector`, `static_vector`, `list` and `slist`.

[endsect]

[section:release_notes_boost_1_61_00 Boost 1.61 Release]

* [classref boost::container::small_vector] supports more constructors and assignments.
* Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/11820 Trac #11820: ['"compiler error when using operator[] of map"]].
   * [@https://svn.boost.org/trac/boost/ticket/11856 Trac #11856: ['"pool_resource.cpp error: declaration changes meaning"]].
   * [@https://svn.boost.org/trac/boost/ticket/11866 Trac #11866: ['"small_vector does not have range constructor"]].
   * [@https://svn.boost.org/trac/boost/ticket/11867 Trac #11867: ['"small_vector should have constructor and assignment operator taking other small_vector"]].
   * [@https://svn.boost.org/trac/boost/ticket/11912 Trac #11912: ['"flat_map use of vector::priv_forward_range_insert_expand_backwards may cause move with same source"]].
   * [@https://svn.boost.org/trac/boost/ticket/11957 Trac #11957: ['"static_vector::max_size() is higher than the capacity"]].
   * [@https://svn.boost.org/trac/boost/ticket/12014 Trac #12014: ['"boost::container::set can not insert const (ref) range"]].
   * [@https://github.com/boostorg/container/pull/33 GitHub #33: ['Make sure std::string constructor is available]].

[endsect]

[section:release_notes_boost_1_60_00 Boost 1.60 Release]

* Implemented [link container.cpp_conformance.polymorphic_memory_resources Polymorphic Memory Resources].
* Add more BOOST_ASSERT checks to test preconditions in some operations (like `pop_back`, `pop_front`, `back`, `front`, etc.)
* Added C++11 `back`/`front` operations to [classref boost::container::basic_string basic_string].
* Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/11627 Trac #11627: ['"small_vector<T,n>::swap() appears to be broken"]].
   * [@https://svn.boost.org/trac/boost/ticket/11628 Trac #11628: ['"small_vector<int,n> iterates over elements in destructor"]].
   * [@https://svn.boost.org/trac/boost/ticket/11697 Trac #11697: ['"Wrong initialization order in tuple copy-constructor"]].
   * [@https://svn.boost.org/trac/boost/ticket/11698 Trac #11698: ['"Missing return statement in static_storage_allocator"]].
   * [@https://github.com/boostorg/container/pull/29 GitHub #29: ['Doc fixes for flap_map complexity requirements]].
   * [@https://github.com/boostorg/container/pull/31 GitHub #31: ['DL_SIZE_IMPL also dereference addr]].

[endsect]

[section:release_notes_boost_1_59_00 Boost 1.59 Release]

* [@https://github.com/boostorg/container/pull/26 GitHub #26: ['Fix bug in stable_vector::capacity()]]. Thanks to timsong-cpp/Arindam Mukerjee.
* [@https://github.com/boostorg/container/pull/27 GitHub #27: ['fix stable_vector's index_of's doxygen comment]]. Thanks to kariya-mitsuru.
* [@https://svn.boost.org/trac/boost/ticket/11380 Trac #11380: ['"Container library std forward declarations incorrect in std_fwd.hpp on libc++ with gcc"]].
* [@https://svn.boost.org/trac/boost/ticket/11388 Trac #11388: ['"boost::container::list::emplace_back broken on Visual Studio 2010"]].
* [@https://svn.boost.org/trac/boost/ticket/11339 Trac #11339: ['"VC12 LNK2005 error with boost::container::adaptive_pool"]].

[endsect]

[section:release_notes_boost_1_58_00 Boost 1.58 Release]
*  Experimental [classref boost::container::small_vector small_vector] container.
*  Massive dependency reorganization. Now [*Boost.Container] depends on very basic utilities like Boost.Core
   and [*Boost.Intrusive]. Preprocessed code size have decreased considerably and compilation times have improved.
*  Added `nth` and `index_of` functions to containers with random-access iterators (except `basic_string`).
*  Added C++17's `allocator_traits<Allocator>::is_always_equal`.
*  Updated containers to implement new constructors as specified in
   [@http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2210 2210. Missing allocator-extended constructor for allocator-aware containers].
*  Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/9931  Trac #9931: ['"flat_map::insert(ordered_unique_range_t...) fails with move_iterators"]] (reopened).
   * [@https://svn.boost.org/trac/boost/ticket/11076 Trac #11076: ['"Unqualified calls to memmove/memcpy in container/detail/copy_move_algo.hpp"]].
   * [@https://svn.boost.org/trac/boost/ticket/10790 Trac #10790 (['"long long errors from container"])].
   * [@https://svn.boost.org/trac/boost/ticket/10808 Trac #10808 (['"compare equal operator of vector is broken"])].
   * [@https://svn.boost.org/trac/boost/ticket/10930 Trac #10930 (['"container std_fwd.hpp neglects custom std namespaces"])].
   * [@https://svn.boost.org/trac/boost/ticket/11139 Trac #11139 (['"boost::container::vector<std::shared_ptr<const T>...>::const_iterator allows changing dereferenced elements"])].
* [*Source Breaking]: [classref boost::container::scoped_allocator_adaptor scoped_allocator_adaptor]'s
   `propagate_on_container_copy_assignment`, `propagate_on_container_move_assignment` and `propagate_on_container_swap`
   are no longer `::boost::integral_constant<bool, true/false>` types. The dependency reorganization needed to break
   with those classes to avoid MPL dependencies, and interoperability with `std::integral_constant` was not guaranteed.
   Code assumming `boost::true_type/boost::false_type` on this will not compile. As a workaround, use the guaranteed internal
   `::value` constant: `::boost::integral_constant<bool, scoped_allocator_adaptor<Allocator>::propagate_on_container_move_assignment::value>`.

[endsect]

[section:release_notes_boost_1_57_00 Boost 1.57 Release]
*  Added support for `initializer_list`. Contributed by Robert Matusewicz.
*  Fixed double destruction bugs in vector and backward expansion capable allocators.
*  Fixed bugs:
   * [@https://svn.boost.org/trac/boost/ticket/10263 Trac #10263 (['"AIX 6.1 bug with sched_yield() function out of scope"])].
   * [@https://github.com/boostorg/container/pull/16 GitHub #16: ['Fix iterators of incomplete type containers]]. Thanks to Mikael Persson.

[endsect]

[section:release_notes_boost_1_56_00 Boost 1.56 Release]

* Added DlMalloc-based [link container.extended_allocators Extended Allocators].

* [link container.configurable_containers.configurable_tree_based_associative_containers Improved configurability]
   of tree-based ordered associative containers. AVL, Scapegoat and Splay trees are now available
   to implement [classref boost::container::set set], [classref boost::container::multiset multiset],
   [classref boost::container::map map] and [classref boost::container::multimap multimap].

* Fixed bugs:
   *  [@https://svn.boost.org/trac/boost/ticket/9338 #9338: ['"VS2005 compiler errors in swap() definition after including container/memory_util.hpp"]].
   *  [@https://svn.boost.org/trac/boost/ticket/9637 #9637: ['"Boost.Container vector::resize() performance issue"]].
   *  [@https://svn.boost.org/trac/boost/ticket/9648 #9648: ['"string construction optimization - char_traits::copy could be used ..."]].
   *  [@https://svn.boost.org/trac/boost/ticket/9801 #9801: ['"I can no longer create and iterator_range from a stable_vector"]].
   *  [@https://svn.boost.org/trac/boost/ticket/9915 #9915: ['"Documentation issues regarding vector constructors and resize methods - value/default initialization"]].
   *  [@https://svn.boost.org/trac/boost/ticket/9916 #9916: ['"Allocator propagation incorrect in the assignment operator of most"]].
   *  [@https://svn.boost.org/trac/boost/ticket/9931 #9931: ['"flat_map::insert(ordered_unique_range_t...) fails with move_iterators"]].
   *  [@https://svn.boost.org/trac/boost/ticket/9955 #9955: ['"Using memcpy with overlapped buffers in vector"]].

[endsect]

[section:release_notes_boost_1_55_00 Boost 1.55 Release]

*  Implemented [link container.unique_features.scary_iterators SCARY iterators].

*  Fixed bugs [@https://svn.boost.org/trac/boost/ticket/8269 #8269],
              [@https://svn.boost.org/trac/boost/ticket/8473 #8473],
              [@https://svn.boost.org/trac/boost/ticket/8892 #8892],
              [@https://svn.boost.org/trac/boost/ticket/9009 #9009],
              [@https://svn.boost.org/trac/boost/ticket/9064 #9064],
              [@https://svn.boost.org/trac/boost/ticket/9092 #9092],
              [@https://svn.boost.org/trac/boost/ticket/9108 #9108],
              [@https://svn.boost.org/trac/boost/ticket/9166 #9166].

* Added `default initialization` insertion functions to vector-like containers
   with new overloads taking `default_init_t` as an argument instead of `const value_type &`.

[endsect]

[section:release_notes_boost_1_54_00 Boost 1.54 Release]

*  Added experimental `static_vector` class, based on Andrew Hundt's and Adam Wulkiewicz's
   high performance `varray` class.
*  Speed improvements in `vector` constructors/copy/move/swap, dispatching to memcpy when possible.
*  Support for `BOOST_NO_EXCEPTIONS` [@https://svn.boost.org/trac/boost/ticket/7227 #7227].
*  Fixed bugs [@https://svn.boost.org/trac/boost/ticket/7921 #7921],
              [@https://svn.boost.org/trac/boost/ticket/7969 #7969],
              [@https://svn.boost.org/trac/boost/ticket/8118 #8118],
              [@https://svn.boost.org/trac/boost/ticket/8294 #8294],
              [@https://svn.boost.org/trac/boost/ticket/8553 #8553],
              [@https://svn.boost.org/trac/boost/ticket/8724 #8724].

[endsect]

[section:release_notes_boost_1_53_00 Boost 1.53 Release]

*  Fixed bug [@https://svn.boost.org/trac/boost/ticket/7650 #7650].
*  Improved `vector`'s insertion performance.
*  Changed again experimental multiallocation interface for better performance (still experimental).
*  Added no exception support for those willing to disable exceptions in their compilers.
*  Fixed GCC -Wshadow warnings.
*  Replaced deprecated BOOST_NO_XXXX with newer BOOST_NO_CXX11_XXX macros.

[endsect]

[section:release_notes_boost_1_52_00 Boost 1.52 Release]

*  Improved `stable_vector`'s template code bloat and type safety.
*  Changed typedefs and reordered functions of sequence containers to improve doxygen documentation.
*  Fixed bugs
  [@https://svn.boost.org/trac/boost/ticket/6615 #6615],
  [@https://svn.boost.org/trac/boost/ticket/7139 #7139],
  [@https://svn.boost.org/trac/boost/ticket/7215 #7215],
  [@https://svn.boost.org/trac/boost/ticket/7232 #7232],
  [@https://svn.boost.org/trac/boost/ticket/7269 #7269],
  [@https://svn.boost.org/trac/boost/ticket/7439 #7439].
*  Implemented LWG Issue #149 (range insertion now returns an iterator) & cleaned up insertion code in most containers
*  Corrected aliasing errors.

[endsect]

[section:release_notes_boost_1_51_00 Boost 1.51 Release]

*  Fixed bugs
  [@https://svn.boost.org/trac/boost/ticket/6763 #6763],
  [@https://svn.boost.org/trac/boost/ticket/6803 #6803],
  [@https://svn.boost.org/trac/boost/ticket/7114 #7114],
  [@https://svn.boost.org/trac/boost/ticket/7103 #7103].
  [@https://svn.boost.org/trac/boost/ticket/7123 #7123],

[endsect]

[section:release_notes_boost_1_50_00 Boost 1.50 Release]

*  Added Scoped Allocator Model support.

*  Fixed bugs
  [@https://svn.boost.org/trac/boost/ticket/6606 #6606],
  [@https://svn.boost.org/trac/boost/ticket/6533 #6533],
  [@https://svn.boost.org/trac/boost/ticket/6536 #6536],
  [@https://svn.boost.org/trac/boost/ticket/6566 #6566],
  [@https://svn.boost.org/trac/boost/ticket/6575 #6575],

[endsect]


[section:release_notes_boost_1_49_00 Boost 1.49 Release]

*  Fixed bugs
  [@https://svn.boost.org/trac/boost/ticket/6540 #6540],
  [@https://svn.boost.org/trac/boost/ticket/6499 #6499],
  [@https://svn.boost.org/trac/boost/ticket/6336 #6336],
  [@https://svn.boost.org/trac/boost/ticket/6335 #6335],
  [@https://svn.boost.org/trac/boost/ticket/6287 #6287],
  [@https://svn.boost.org/trac/boost/ticket/6205 #6205],
  [@https://svn.boost.org/trac/boost/ticket/4383 #4383].

*  Added `allocator_traits` support for both C++11 and C++03
   compilers through an internal `allocator_traits` clone.

[endsect]

[section:release_notes_boost_1_48_00 Boost 1.48 Release]

*  First release. Container code from [*Boost.Interprocess] was deleted
   and redirected to [*Boost.Container ] via using directives.

[endsect]

[endsect]

[endsect]
