Log message:
boost: Update to 1.75.0

Changelog:
1.75.0
New Libraries

  * JSON: JSON parsing, serialization, and DOM in C++11, from Vinnie Falco and
    Krystian Stasiowski.
      + Fast compilation requiring only C++11
      + Easy and safe modern API with allocator support
      + Compile without Boost, define BOOST_JSON_STANDALONE
      + Optional header-only, without linking to a library
  * LEAF: A lightweight error-handling library for C++11, from Emil Dotchevski.
      + Small single-header format, no dependencies.
      + Designed for maximum efficiency ("happy" path and \ 
"sad" path).
      + No dynamic memory allocations, even with heavy payloads.
      + O(1) transport of arbitrary error types (independent of call stack
        depth).
      + Can be used with or without exception handling.
  * PFR: Basic reflection without macro or boilerplate code for user defined
    types, from Antony Polukhin.

Updated Libraries

  * Asio:
      + Enabled support for UNIX domain sockets on Windows.
      + Added executor-converting construction and assignment to ip::
        basic_resolver.
      + Added compatibility between polymorphic executors and the (deprecated)
        handler invocation hook.
      + Added the experimental::as_single completion token adapter.
      + Added support for MSG_NOSIGNAL on more platforms by using
        _POSIX_VERSION to detect whether it is supported.
      + Added the ability to compile using libpthread on Windows.
      + Added workarounds for the Intel C++ compiler.
      + Added more support for detecting and optimising for handlers that have
        no custom executor.
      + Reduced lock contention for timer cancellation on Windows.
      + Reinstated a previously removed null-pointer check, as it had a
        measurable impact on performance.
      + Fixed the executor concept to test for a const-qualified execute().
      + Fixed any_executor support for builds without RTTI support.
      + Fixed the thread_pool unit test to work without RTTI support.
      + Fixed C++20 coroutines compatibility with clang on Windows.
      + Fixed some compatibility issues with Windows Runtime.
      + Fixed shadow name warnings caused by addition of asio::query.
      + Fixed a "logical ‘or’ of equal expressions" warning on linux.
      + Fixed a benign switch fallthrough warning.
      + Added missing push/pop_options.hpp includes.
      + Suppressed zero-as-null-pointer-constant warnings.
      + Fixed a comma-operator warning.
      + Updated the documentation to clarify when the select reactor is used on
        Windows.
      + Fixed potential ambiguity caused by any_executor comparisons and
        conversion.
      + Added detection of non-experimental C++20 coroutines on MSVC 19.8.
      + Fixed compatibility with uClibc.
      + Fixed strand<> adaptation of Networking TS executors when targeting
        older C++ versions or less conformant compilers.
      + Consult the Revision History for further details.
  * Atomic:
      + Implemented SSE2 and SSE4.1 versions of address lookup algorithm, which
        is used in the internal lock pool implementation. This may improve
        performance of waiting and notifying operations in heavily contended
        cases.
      + Fixed a possible compilation error on AArch64 targets caused by
        incorrect instructions generated for bitwise (logical) operations with
        immediate constants. (#41)
  * Beast:
      + This update brings bug fixes and support for the
        BOOST_ASIO_ENBALE_HANDLER_TRACKING compile flag from Boost.Asio:
      + We'd love to know how you or your company use Beast, consider adding an
        entry to the Companies and Individuals Using Beast list.
      + See the full Release Notes for a complete list of changes.
  * Container:
      + New devector container.
      + Fixed bugs/issues:
          o #152 Tree-based containers have troubles with move-only types.
          o #156 Compile error with vector.
          o PR#157 Add missing include.
          o #159: pmr::monotonic_buffer_resource crashes on large single
            allocations.
          o #160: Usage of uses_allocator needs a remove_cvref_t.
          o #162: small_vector on MSVC x86 call-by-value crash.
          o #161: polymorphic_allocator(memory_resource*) non-standard
            extension causes headache.
          o PR#163: container_rebind for small_vector with options.
          o #165: Link error with shared library and memory_resource inline
            members.
          o PR#166: Fix encoding error in copyright headers.
          o PR#167: error: the address of 'msg' will always evaluate as 'true'
            warning with GCC 4.4.
          o #169: flood of warnings building dlmalloc_ext_2_8_6.c on clang11.
  * Endian:
      + endian_arithmetic no longer inherits from endian_buffer
      + When BOOST_ENDIAN_NO_CTORS is defined, the unaligned endian_buffer and
        endian_arithmetic are C++03 PODs, to enable use of __attribute__((
        packed))
  * Filesystem:
      + New: Added creation_time operation, which allows to obtain file
        creation time. (Inspired by PR#134)
      + The returned value of last_write_time(p, ec) operation in case of
        failure has been changed to a minimal value representable by std::
        time_t instead of -1.
      + The returned value of hard_link_count(p, ec) operation in case of
        failure has been changed to static_cast<uintmax_t>(-1) instead of 0.
      + On POSIX systems, file_size will now indicate error code errc::
        function_not_supported if the path resolves to a non-regular file.
        Previously, errc::operation_not_permitted was reported.
      + On Linux, many operations now use statx system call internally, when
        possible, which allows to reduce the amount of information queried from
        the filesystem and potentially improve performance. The statx system
        call was introduced in Linux kernel 4.11.
      + Removed const-qualification from return types of some path methods.
        This could prevent move construction and move assignment at the call
        site in some cases. (#160)
      + On OpenBSD 4.4 and newer, use statvfs system call to obtain filesystem
        space information. (Inspired by PR#162)
      + On Windows, space now returns with an error if the provided path does
        not idendify an existing file. (#167)
  * GIL:
      + BREAKING: In next release, we are going to drop support for GCC 5. We
        may also change the required minimum C++ version from C++11 to C++14.
  * Histogram:
      + This update brings
          o Bug-fixes for corner-cases
          o Small documentation improvements
          o Fixes for new warnings from latest compilers and when compiling
            against the C++20 standard
      + See the full Release Notes for a complete list of changes.
  * Interprocess:
      + Fixed bugs:
          o #127: static assertion failure with boost interprocess 1.74 and
            basic_managed_shared_memory.
  * Intrusive:
      + Fixed bugs:
          o PR#48: MSVC "assignment within conditional" warning fix.
          o PR#49: Fix empty control statement warnings.
          o #52: Invalid casting in BOOST_INTRUSIVE_BSR_INTRINSIC.
  * Log:
      + Bug fixes:
          o Corrected the file counter that would be used in text_file_backend
            when generating the target file name (based on the pattern set by
            set_target_file_name_pattern method) when the log file is rotated.
            (#125)
          o Replaced a volatile version counter in basic_sink_frontend with an
            atomic. (#128)
          o In the asynchronous_sink frontend, resolved a possible conflict
            between flush and run methods, if run is called from a user's
            thread instead of the internal dedicated thread spawned by the
            frontend. (#131)
      + See changelog for more details.
  * Move:
      + Fixed bugs:
          o #30: (void) C-cast is a non-portable way of suppressing compiler
            warnings.
  * Mp11:
      + Added mp_pairwise_fold (suggested by Barry Revzin)
      + Removed mp_invoke (use mp_invoke_q)
  * Optional:
      + boost::none is constexpr-declared.
      + Fixed issue #78.
  * Outcome:
      + Announcements:
          o After a year and three major Boost releases announcing this
            upcoming change, this is the FINAL RELEASE of the v2.1 branch. From
            Boost 1.76 onwards, the v2.2 branch becomes the default. This
            branch has a number of major breaking changes to Outcome v2.1, see
            the documentation for details.
      + Enhancements:
          o The ADL discovered event hooks have been replaced with
            policy-specified event hooks instead. This is due to brittleness
            (where hooks would quietly self-disable if somebody changed
            something), compiler bugs (a difference in compiler settings causes
            the wrong hooks, or some but not all hooks, to get discovered), and
            end user difficulty in using them at all. The policy-specified
            event hooks can be told to default to ADL discovered hooks for
            backwards compatibility: set OUTCOME_ENABLE_LEGACY_SUPPORT_FOR to
            less than 220 to enable emulation.
          o Improve configuring OUTCOME_GCC6_CONCEPT_BOOL. Older GCCs had
            boolean based concepts syntax, whereas newer GCCs are standards
            conforming. However the precise logic of when to use legacy and
            conforming syntax was not well understood, which caused Outcome to
            fail to compile depending on what options you pass to GCC. The new
            logic always uses the legacy syntax if on GCC 8 or older, otherwise
            we use conforming syntax if and only if GCC is in C++ 20 mode or
            later. This hopefully will resolve the corner case build failures
            on GCC.
      + Bug fixes:
          o Boost.Outcome should now compile with BOOST_NO_EXCEPTIONS defined.
            Thanks to Emil, maintainer of Boost.Exception, making a change for
            me, Boost.Outcome should now compile with C++ exceptions globally
            disabled. You won't be able to use boost::exception_ptr as it can't
            be included if C++ exceptions are globally disabled.
          o #236 In the Coroutine support the final_suspend() was not noexcept,
            despite being required to be so in the C++ 20 standard. This has
            been fixed, but only if your compiler implements noop_coroutine.
            Additionally, if noop_coroutine is available, we use the much more
            efficient coroutine handle returning variant of await_suspend()
            which should significantly improve codegen and context switching
            performance.
  * Polygon:
      + C++20 fixes for event_comparison_type, vertex_equality_predicate_type,
        and voronoi_predicates. (Glen Fernandes)
  * Preprocessor:
      + When variadic data is empty in C++20 mode with __VA_OPT__ support the
        variadic size has been corrected to be 0. This also means that in this
        C++20 mode it is now valid to convert to and from empty arrays and
        lists and variadic data. The end-user can read the "C++20 Support For
        Variadic Macros" part of the "variadic macros" topic for more
        information about empty variadic data in the library.
      + The macro BOOST_PP_IS_STANDARD() has been added for identifying if the
        currently used preprocessor is a C++ standard conforming preprocessor.
        A number of preprocessors which generally work correctly with the
        library but need various internal workarounds, including the currently
        default VC++ preprocessor, are not considered C++ standard conforming
        preprocessors. However most preprocessors, including among others gcc,
        clang, and the new but currently non-default VC++ preprocessor in
        VS2019, are C++ standard conforming preprocessors.
      + For C++ standard conforming preprocessors a number of the limits
        defined in the config/limits.hpp can now be changed to higher amounts
        for a TU. The end-user should read the "limitations" topic to
        understand how and which limits can be changed.
      + For C++ standard conforming preprocessors, in order to allow the
        maximum number of FOR and WHILE iterations, the beginning 'r' and 'd'
        iteration numbers in the user-defined macros start at 1 and not 2, as
        it did in previous releases. This could be a breaking change if these
        iteration numbers are used in the user-defined macros ( they probably
        would not be ), but the change was necessary to fix some arcane bugs
        when dealing with numerical/logical operations with maximum numbers as
        well to allow the user-defined macros to be called the correct possible
        maximum number of times. For non-C++ conforming preprocessors, this
        change was not made because those non-conforming C++ preprocessors
        generally have limitations which disallow the maximum number of looping
        constructs to be run, and it was felt not to introduce a possible
        breaking change to those more fragile preprocessors would be better. It
        was also felt that besides fixing some arcane preprocessor bugs and
        providing the possible maximum number of user-defined macro
        invocations, this change could be made because it has never been
        documented what the starting 'r' and 'd' iteration numbers actually are
        but only that these numbers are incremented for each iteration.
      + The library has been upgraded to assume variadic macro support for any
        compiler working with the library. Ostensibly this means that the
        library is now a C++11 on up library, yet most of the major compilers,
        including gcc, clang, and VC++, also support variadic macros in C++98/
        C++03 mode as long as strict compliance to C++98/C++03 is not turned on
        when using one of those compilers.
  * Rational:
      + Fix Rational operators to not break under new C++20 operator==
        rewriting rules. (Glen Fernandes)
  * Signals2:
      + Correct C++ allocator model support to fix compilation in C++20
        standards mode. (Glen Fernandes)
  * System:
      + The platform-specific headers windows_error.hpp, linux_error.hpp, and
        cygwin_error.hpp emit deprecation messages and are slated for removal.
      + The old names for generic_category() and system_category() emit
        deprecation messages and are slated for removal.
      + error_condition::failed is deprecated and is slated for removal.
        operator bool() for error_condition has been reverted to its old
        meaning of value() != 0. This is done for compatibility with std::
        error_condition as the next release is expected to improve
        interoperability with <system_error> even further. Note that this does
        not affect error_code::failed, which is still alive and well.
      + The overload of error_condition::message that takes a buffer is
        deprecated and is slated for removal, for the same reasons. Note that
        this does not affect error_code::message.
  * uBLAS:
      + Correct C++ allocator model support to fix compilation in C++20
        standards mode. (Glen Fernandes and Conrad Poelman)
  * VMD:
      + The VMD number parsing has been upgraded to support the ability for the
        end-user to change the number limits in the Preprocessor library.
      + The macro BOOST_VMD_IS_GENERAL_IDENTIFIER has been added to support the
        parsing of input that represents a preprocessor token which matches the
        VMD identifier syntax, without having to register the identifier as a
        specific identifier.
  * Wave:
      + Added new C++20 tokens, including the spaceship operator <=>
      + Fixed bugs:
          o #94: fix incorrect behavior of __LINE__ and __FILE__ under
            rescanning

1.74.0
New Libraries

  * STLInterfaces: A library of CRTP bases to ease the writing of STL views,
    iterators, and sequence containers, from Zach Laine.

Updated Libraries

  * Asio:
      + Added an implementation of the proposed standard executors (P0443r13,
        P1348r0, and P1393r0).
      + Added support for the proposed standard executors to Asio's I/O
        facilities.
          o The supplied executors now meet the requirements for the proposed
            standard executors. These classes also continue to meet the
            existing requirements for the Networking TS model of executors.
          o All I/O objects, asynchronous operations, and utilities will
            interoperate with both new proposed standard executors, and with
            existing Networking TS executors.
          o The any_io_executor type alias has been introduced as the default
            runtime-polymorphic executor for all I/O objects. This defaults to
            the execution::any_executor<> template. If required for backward
            compatibility, BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT can be defined
            to use the old asio::executor polymorphic wrapper instead.
          o Support for the existing Networking TS model of executors can be
            disabled by defining BOOST_ASIO_NO_TS_EXECUTORS.
      + Added converting move construction and assignment to
        basic_waitable_timer.
      + Enabled C++20 coroutine support when using gcc 10.
      + Added overloads of co_spawn that launch an awaitable.
      + Added a new constructor overload to use_awaitable_t's default executor
        adapter, to enable conversion between executor types.
      + Added support for using detached_t as a default completion token, by
        adding members as_default_on() and as_default_on_t<>.
      + Added a move constructor to ssl::stream<>.
      + Changed ssl::stream<> write operations to linearise gather-write buffer
        sequences.
      + Added compile-time detection of the deprecated asio_handler_invoke,
        asio_handler_allocate, and asio_handler_deallocate hooks, when
        BOOST_ASIO_NO_DEPRECATED is defined.
      + Implemented a number of performance optimisations.
      + Added source location support to handler tracking.
      + Implemented various improvements to the handlerviz.pl tool.
      + Added the handlerlive.pl tool, which processes handler tracking output
        to produce a list of "live" handlers.
      + Added the handlertree.pl tool, which filters handler tracking output to
        include only those events in the tree that produced the nominated
        handlers.
      + Added changes for clang-based Embarcadero C++ compilers.
      + Fixed a deadlock that can occur when multiple threads concurrently
        initialise the Windows I/O completion port backend.
      + Fixed async_compose to work with copyable handlers when passed by
        lvalue.
      + Fixed completion signature deduction in co_spawn.
      + Removed a spurious Executor base class from the executor_binder
        implementation.
      + Various fixes and improvements in the documentation and examples.
      + Consult the Revision History for further details.
  * Atomic:
      + Added missing const qualifiers to some operations in atomic_ref.
      + Added support for yield instruction on ARMv8-A. The instruction is used
        internally in spin loops to reduce CPU power consumption.
      + Added support for C++20 waiting and notifying operations. The
        implementation includes generic backend that involves the internal lock
        pool, as well as specialized backends for Windows, Linux, FreeBSD,
        DragonFly BSD and NetBSD. Atomic types provide a new method
        has_native_wait_notify, a static boolean constant
        always_has_native_wait_notify and a set of capability macros that allow
        to detect if the implementation supports native waiting and notifying
        operations for a given type.
      + Changed internal representation of atomic_flag to use 32-bit storage.
        This allows for more efficient waiting and notifying operations on
        atomic_flag on some platforms.
      + Added support for build-time configuration of the internal lock pool
        size. The user can define the BOOST_ATOMIC_LOCK_POOL_SIZE_LOG2 macro to
        specify binary logarithm of the size of the lock pool. The default
        value is 8, meaning that the size of the lock pool is 256, up from 64
        used in the previous release.
      + Added support for a new set of atomic types dedicated for inter-process
        communication: ipc_atomic_flag, ipc_atomic and ipc_atomic_ref. Users
        are recommended to port their code using non-IPC types for
        inter-process communication to the new types. The new types provide the
        same set of operations as their non-IPC counterparts, with the
        following differences:
          o Most operations have an added precondition that is_lock_free
            returns true for the given atomic object. The library will issue a
            compile time error if this precondition is known to be not
            satisfied at compile time.
          o All provided operations are address-free, meaning that the atomic
            object (in case of ipc_atomic_ref - the referenced object) may be
            located in process-shared memory or mapped into the same process at
            multiple different addresses.
          o The new has_native_wait_notify operation and
            always_has_native_wait_notify constant indicate support for native
            inter-process waiting and notifying operations. When that support
            is not present, the operations are implemented with a busy loop,
            which is less efficient, but still is address-free. A separate set
            of capability macros is also provided to indicate this support.
      + Added new atomic_unsigned_lock_free and atomic_signed_lock_free types
        introduced in C++20. The types indicate the atomic object type for an
        unsigned or signed integer, respectively, that is lock-free and
        preferably has native support for waiting and notifying operations.
      + Added new gcc assembler backends for ARMv8-A (for both AArch32 and
        AArch64). The new backends are used to implement operations not
        supported by compiler intrinsics (including 128-bit operations on
        AArch64) and can also be used when compiler intrinsics are not
        available. Both little and big endian targets are supported. AArch64
        backend supports extensions defined in ARMv8.1 and ARMv8.3.
      + Added support for big endian targets in the legacy ARM backend based on
        gcc assembler blocks (this backend is used on ARMv7 and older targets).
        Previously, the backend assumed little endian memory layout, which is
        significant for 64-bit operations.
      + Improved performance of seq_cst stores and thread fences on x86 by
        using lock-prefixed instructions instead of mfence. This means that the
        operations no longer affect non-temporal stores, which was also not
        guaranteed before. Use specialized instructions and intrinsics to order
        non-temporal memory accesses.
      + Fixed capability macros for 80-bit long double on x86 targets not
        indicating lock-free operations even if 128-bit atomic operations were
        available.
      + Fixed compilation of gcc asm blocks on Alpha targets.
      + In the gcc __sync* intrinsics backend, fixed that store and load
        operations of large objects (larger than a pointer size) could be
        non-atomic. The implementation currently assumes that small objects can
        be stored with a single instruction atomically on all modern
        architectures.
  * Beast:
      + This update brings bug fixes and support for the following changes
        changes in Boost.Asio:
      + Beast supports BOOST_ASIO_NO_DEPRECATED. Define this to help identify
        areas of your Beast and Asio code which use deprecated Asio interfaces.
      + Beast also supports BOOST_ASIO_NO_TS_EXECUTORS. Define this to identify
        uses of executors from the now potentially outdated Networking TS
      + Asio will use the Standard Executors model by default. You can prevent
        this behaviour by defining BOOST_ASIO_USE_TS_EXECUTOR_AS_DEFAULT in
        which the Networking TS model will be used by default. Setting this
        flag does not prevent a program from using executors from the Standard
        Executors model explicitly.
      + We'd love to know how you or your company use Beast, consider adding an
        entry to the Companies and Individuals Using Beast list.
      + See the full Release Notes for a complete list of changes.
  * Bimap:
      + Correct allocator usage (fixes C++20 compilation). (Glen Fernandes)
  * Config:
      + Implement BOOST_NO_CXX11_OVERRIDE and BOOST_OVERRIDE. (Glen Fernandes)
  * Core:
      + Implemented the allocator access utilities which provide a replacement
        for allocator_traits with individual traits and functions for each
        facility. They support the C++11 allocator model when possible and
        provide a fallback for C++98 compatibility. These are now used in
        Circular_Buffer, Wave, Lockfree, Heap, Smart_Ptr, Dynamic_Bitset,
        Format, Bimap and more. (Glen Fernandes)
  * DLL:
      + Multiple fixes for the library_info work on empty shared objects.
      + Compilation fixes for C++98 and C++11 modes (#28).
      + Fixes for smart_library manglings (thanks to XiaLiChao82 #37).
  * Endian:
      + Enabled scoped enumeration types in endian_reverse.
      + Enabled bool, enum, float, double in endian_reverse_inplace.
      + Added an overload of endian_reverse_inplace for arrays.
  * Filesystem:
      + Removed compile-time checks for support for symlinks and hardlink on
        Windows. Instead, a runtime check is used. (PR#142)
      + Fixed handling of reparse points in canonical and read_symlink on
        Windows. This also affects other algorithms that involve canonical and
        read_symlink in their implementation. (PR#100, #85, #99, #123, #125)
      + Fixed that read_symlink on Windows could potentially fail or cause
        failures elsewhere with a sharing violation error, if the same symlink
        was opened concurrently. (#138)
      + Fixed that is_symlink(directory_entry) would always return false, even
        if the directory entry actually referred to a symlink. (PR#148)
      + Added missing status inspection operation overloads for directory_entry
        and error_code (e.g. is_directory(directory_entry, error_code&)).
        Removed incorrect noexcept specifications for the overloads not taking
        the error_code arguments.
      + copy_file implementation has been updated to perform checks on the
        source and target files, as required by C++20 ([fs.op.copy.file]/4.1).
        In particular, the operation will fail if the source or target file is
        not a regular file or the source and target paths identify the same
        file.
      + copy_file on POSIX systems will now also copy the source file
        permissions to the target file, if the target file is overwritten.
      + New: Added copy_file implementations based on sendfile and
        copy_file_range system calls on Linux, which may improve file copying
        performance, especially on network filesystems.
      + Deprecated: The copy_option enumeration that is used with the copy_file
        operation is deprecated. As a replacement, the new enum copy_options
        (note the trailing 's') has been added. The new enum contains values
        similar to the copy_options enum from C++20. The old enum values are
        mapped onto the new enum. The old enum will be removed in a future
        release.
      + New: Added copy_options::skip_existing option, which allows copy_file
        operation to succeed without overwriting the target file, if it exists.
      + New: Added copy_options::update_existing option, which allows copy_file
        operation to conditionally overwrite the target file, if it exists, if
        its last write time is older than that of the replacement file.
      + New: copy_file now returns bool, which indicates whether the file was
        copied.
      + New, breaking change: copy operation has been extended and reworked to
        implement behavior specified in C++20 [fs.op.copy]. This includes
        support for copy_options::recursive, copy_options::copy_symlinks,
        copy_options::skip_symlinks, copy_options::directories_only,
        copy_options::create_symlinks and copy_options::create_hard_links
        options. The operation performs additional checks based on the
        specified options. Applying copy to a directory with default
        copy_options will now also copy files residing in that directory (but
        not nested directories or files in those directories).
      + New: Added create_directory overload taking two paths. The second path
        is a path to an existing directory, which is used as a source of
        permission attributes to use in the directory to create.
      + Deprecated: copy_directory operation has been deprecated in favor of
        the new create_directory overload. Note that the two operations have
        reversed order of the path arguments.
      + equivalent on POSIX systems now returns the actual error code from the
        OS if one of the paths does not resolve to a file. Previously the
        function would return an error code of 1. (#141)
      + equivalent no longer considers file size and last modification time in
        order to test whether the two paths refer to the same file. These
        checks could result in a false negative if the file was modified during
        the equivalent call.
      + New: Added absolute overloads taking error_code argument.
      + Operations that have current_path() as the default value of their
        arguments and also have an error_code argument will use the
        current_path(error_code& ec) overload to obtain the current path, so
        that its failure is reported via the error_code argument instead of an
        exception.
      + space now initializes the space_info structure members to -1 values on
        error, as required by C++20 ([fs.op.space]/1).
      + space on Windows now accepts paths referring to arbitrary files, not
        only directories. This is similar to POSIX systems and corresponds to
        the operation description in C++20. (#73)
      + New: Added implementation of temp_directory_path for Windows CE. (PR#25
        )
      + New: Improved compatibility with WASI platform. (PR#144)
      + New: Improved support for Embarcadero compilers. (PR#130)
      + New: Added implementations of unique_path operation based on getrandom
        (Linux), arc4random_buf (OpenBSD/FreeBSD/CloudABI) and BCrypt (Windows)
        system APIs.
      + Deprecated: Auto-linking against system libraries on Windows with
        MSVC-compatible compilers is deprecated and will be removed in a future
        release. This affects users linking against static library of
        Boost.Filesystem. Users are advised to update their project build
        systems to either use a shared library of Boost.Filesystem, or
        explicitly specify the dependencies of Boost.Filesystem in the linker
        command line. Users of shared library of Boost.Filesystem are not
        affected.
  * Flyweight:
      + Maintenance work.
  * Format:
      + Correct allocator usage (fixes C++20 compilation). (Glen Fernandes)
  * Geometry:
      + Improvements
          o PR#720 Additional R-tree constructors (thanks to Caian Benedicto).
          o Various improvements in buffer, set and relational operations.
      + Solved issues
          o #709 memcpy called for object with no trivial copy-assignment.
          o #721 Compilation error in bgi::detail::rtree::visitors::insert.
          o #727 MSVC warning: conditional expression is constant.
      + Bugfixes
          o PR#700 Missing cases for default strategies in distance algorithm.
          o PR#738 Longitudes out of range in direct geodesic formulas.
  * GIL:
      + Added
          o Added new constructor initializing any_image from r-value reference
            to any image (PR#486).
          o Implemented mechanism to reverse kernel_2d (PR#489).
      + Changed
          o BREAKING: Replace Boost.Variant with Boost.Variant2 (PR#474) which
            completes removal on uses of Boost.MPL (missing from Boost 1.72.0
            change added PR#274).
          o Use perfect forwarding from apply_operation to visit (PR#491).
      + Removed
          o BREAKING: Removed dependency on Boost.Variant
      + Fixed
          o Fixed invalid conversion from RGB8 to CMYK32 due to overflow (PR#
            470).
          o Fixed image constructor from other image (PR#477).
          o Fixed error plane_view_t is not a class or namespace name (PR#481).
          o Fixed interleaved_view factory using point<std::ptrdiff_t> for
            dimension (PR#487).
          o Fixed documentation replacing uses MPL with MP11 in tutorial (PR#
            494).
          o Fixed missing header in numeric/kernel.hpp to make it
            self-contained (PR#502).
      + Acknowledgements
          o Samuel Debionne, Pranam Lashkari, Mateusz Loskot, Debabrata Mandal
  * Heap:
      + Correct destruction of top node in skew_heap. (Glen Fernandes)
      + Correct and simplify allocator use. (Glen Fernandes)
  * Integer:
      + Fixed compilation of gcd in C++20 mode with clang 10.
      + Improved support for Embarcadero compilers. (PR#21)
  * Iterator:
      + boost/function_output_iterator.hpp header is now deprecated. Users
        should replace its inclusion with boost/iterator/
        function_output_iterator.hpp. (PR#51)
      + Improved support for Embarcadero compilers. (PR#55)
  * LexicalCast:
      + Fixed warnings on missing override (thanks to EugeneZelenko #35, #34).
      + Fixes for the the Embarcadero compilers (thanks to Edward Diener).
  * Log:
      + Bug fixes:
          o The syslog sink backend now verifies the IP version of the local
            and target addresses set by user. The addresses must have the same
            IP version as was specified in the ip_version named parameter on
            the sink backend construction (by default, IPv4 is assumed). When
            an address is obtained as a result of host name resolution, only
            addresses with matching IP version are considered. (#119)
      + New Features:
          o Move constructors and assignment operators of various components
            were marked noexcept.
          o Added a new range_manip stream manipulator that can be used for
            outputting elements of a range, optionally separated by a
            delimiter.
          o Added a new tuple_manip stream manipulator that can be used for
            outputting elements of a tuple or any other heterogeneous sequence,
            optionally separated by a delimiter.
          o Added a new optional_manip stream manipulator that can be used for
            outputting optionally present values.
      + See changelog for more details.
  * Mp11:
      + Improved compilation performance of mp_with_index<N> for large N.
      + Added tuple_transform (contributed by Hans Dembinski.)
  * Multi-index Containers:
      + Added node extraction and insertion following the analogous interface
        of associative containers as introduced in C++17. This feature has also
        been extended to non key-based indices, in contrast to C++ standard
        library sequence containers, which do not provide such functionality.
      + Clarified documentation on read/write key extractors (issue #32).
      + Maintenance work.
  * Nowide:
      + The library now requires a C++11-compliant compiler and stdlib
      + LFS: Add support for files > 2 GB where the underlying system supports
        it
      + Generic UTF conversion functions are now available in the boost::nowide
        ::utf namespace
      + Add support for stat with UTF-8 paths
  * Outcome:
      + Announcements:
          o The v2.1 branch is expected to be retired end of 2020, with the
            v2.2 branch becoming the default. You can use the future v2.2
            branch now using better_optimisation. This branch has a number of
            major breaking changes to Outcome v2.1, see the front page for
            details.
      + Enhancements:
          o BREAKING CHANGE void results and outcomes no longer default
            construct types during explicit construction. Previously if you
            explicitly constructed a result<T> from a non-errored \ 
result<void>,
            it default constructed T. This was found to cause unhelpful
            surprise, so it has been disabled.
          o New macro OUTCOME_ENABLE_LEGACY_SUPPORT_FOR. The macro
            OUTCOME_ENABLE_LEGACY_SUPPORT_FOR can be used to enable aliasing of
            older naming and features to newer naming and features when using a
            newer version of Outcome.
          o Concepts now have snake case style naming instead of camel case
            style. When Outcome was first implemented, it was thought that C++
            20 concepts were going to have camel case style. This was changed
            before the C++ 20 release, and Outcome's concepts have been renamed
            similarly. This won't break any code in Outcome v2.1, as
            compatibility aliases are provided. However code compiled against
            Outcome v2.2 will need to be upgraded, unless
            OUTCOME_ENABLE_LEGACY_SUPPORT_FOR is set to 210 or lower.
          o Concepts now live in OUTCOME_V2_NAMESPACE::concepts namespace.
            Previously concepts lived in the convert namespace, now they live
            in their own namespace.
          o New concepts basic_result<T> and basic_outcome<T> added. \ 
End users
            were finding an unhelpful gap in between is_basic_result<T> and
            value_or_error<T> where they wanted a concept that matched types
            which were basic_result, but not exactly one of those. Concepts
            filling that gap were added.
          o Operation TRY works differently from Outcome v2.2 onwards. This is
            a severely code breaking change which change the syntax of how one
            uses OUTCOME_TRY(). A regular expression suitable for upgrading
            code can be found in the list of changes between Outcome v2.1 and
            v2.2.
      + Bug fixes:
          o #224 The clang Apple ships in Xcode 11.4 (currently the latest) has
            not been patched with the fixes to LLVM clang that fix noexcept(std
            ::is_constructible<T, void>) failing to compile which I originally
            submitted years ago. So give up waiting on Apple to fix their
            clang, add a workaround to Outcome.
          o Spare storage could not be used from within no-value policy
            classes. Due to an obvious brain fart when writing the code at the
            time, the spare storage APIs had the wrong prototype which
            prevented them working from within policy classes. Sorry.
  * PolyCollection:
      + Fixed internal ambiguity problem between boost::type_erasure::any and
        boost::any (issue #17).
      + Maintenance work.
  * SmartPtr:
      + Added owner_equals to shared_ptr, weak_ptr, local_shared_ptr.
      + Added owner_hash_value to shared_ptr, weak_ptr.
      + Added owner_equal_to, owner_hash.
      + Added std::hash specializations for shared_ptr, local_shared_ptr.
      + Added boost::hash support to, and std::hash, std::equal_to
        specializations for, weak_ptr.
  * Stacktrace:
      + Fixed a build error when compiled with -fno-exceptions (thanks to
        Jeremiah Rodriguez #91).
  * System:
      + operator bool() now returns failed() instead of value() != 0.
  * Type_Traits:
      + Implemented conjunction, disjunction, negation, is_trivially_copyable,
        is_scoped_enum, and is_unscoped_enum. (Glen Fernandes)
  * Variant:
      + Fixed warnings on missing override (thanks to EugeneZelenko #78).
      + Fixes for the the Embarcadero compilers (thanks to Edward Diener #79).
      + Updated header locations to avoid warnings about using deprecated
        headers (thanks to Andrey Semashev #80)
  * Variant2:
      + Added support for derived types in visit.
      + Improved compilation performance for many (hundreds of) alternatives.
      + Added support for visit<R>.
  * Wave:
      + Implement C++20 features for variadics, including __VA_OPT__ (PR#75)
      + Implement __has_include (PR#102)
      + Introduce new sample: check_macro_naming, useful with Boost itself (PR#
        97)
      + Fix compilation issue caused by std::allocator member removal in C++20
        (PR#72)
      + Repair Xpressive lexer and token_statistics sample (PR#79)
      + Repair lexertl lexer (PR#78)
      + Ensure hooks are run on predefined macros as well (PR#87)
      + Various minor bug fixes
      + C++98/03 support is now deprecated and will be removed in 1.77
  * YAP:
      + Fixed compilation errors for placeholders; they now work in the general
        case, and in particular work with yap::print().
      + constexpr all the YAP.
      + Fix printing of correct value category in yap::print().
      + Doc clarification.

Updated Tools

  * Boostbook:
      + Change encoding of generated documentation from US-ASCII to UTF-8.
        (Glen Fernandes)

Log message:
boost-headers: changed dirfd patch to be platform agnostic

Log message:
boost-headers: bump revision for new patches

Log message:
boost: Fix graphics/krita-4.3.0 build

Log message:
boost: updated to 1.73.0

1.73.0:

Known Issues
------------
These are patches from library authors which were found too late to be fixed in \ 
the release. Be careful as they have not been through the normal testing \ 
process.

New Libraries
-------------
Nowide:
Standard library functions with UTF-8 API on Windows, from Artyom Beilis.

StaticString:
A dynamically resizable string of characters with compile-time fixed capacity \ 
and contiguous embedded storage, from Vinnie Falco and Krystian Stasiowski

Updated Libraries
-----------------
Align:
* Update aligned_alloc to support older mingw32.
Any:
* Speedup compilation by not including <algorithm>.
* Maintenance work, including CI hardening.
Asio:
* Fixed compatibility with C++20 concept syntax.
* Marked the POSIX descriptor classes' move constructors as noexcept.
* Added the ssl::host_name_verification class, which is a drop-in replacement \ 
for ssl::rfc2818_verification. The ssl::rfc2818_verification class has been \ 
marked as deprecated. As a consequence of this change, SSL support now depends \ 
on functions that were introduced in OpenSSL 1.0.2.
* Added an ssl::context constructor to take ownership of a native handle.
* Changed C++ language version detection with gcc to use __cplusplus macro.
* Fixed a work counting issue in the asynchronous resolve operation for endpoints.
* Fixed the strand<> converting constructors and assignment operators.
* Ensured that resolvers are restarted correctly after a fork.
* Fixed compatibility with the current NetBSD release.
* Removed spurious handler requirement checks in some async_read overloads.
* Changed the ssl::context class to propagate non-EOF errors from the \ 
add_certificate_authority function.
* Fixed a Windows-specific thread_pool destructor hang that occurred when the \ 
pool had an associated I/O object.
* Changed the select reactor to recreate the "self pipe trick" sockets \ 
on error. This addresses an issue on some versions of Windows, where these \ 
sockets are discconected after a system sleep.
* Fixed a compile error in the buffered streams due to the lack of reference \ 
collapsing in C++98.
* Changed the priority_scheduler example to demonstrate calls to shutdown() and \ 
destroy().
* Removed some unnecessary null pointer checks.
* Changed Windows platform detection to recognise TV titles as Windows apps.
* Added some emscripten compatibility patches.
* Fixed a compile error in the use_awaitable_t::as_default_on function.
* Changed all uses of the boost.bind placeholders to use the boost::placeholders \ 
namespace.
* Fixed a potential compile error in the async_compose implementation due to \ 
incorrect overload selection.
* Suppressed some non-virtual destructor warnings.
* Various documentation fixes and improvements.
Assert:
* Added source_location.
Atomic:
* Implemented C++20 atomic_ref. See docs and especially the caveats section.
* Implemented atomic_flag::test operation, which was introduced in C++20.
* atomic<T> should now take into account alignment requirements of T, \ 
which makes a difference if those requirements are higher than that of the \ 
internal storage of atomic.
* Added static asserts enforcing the requirements on the value type T used with \ 
atomic and atomic_ref. This should prohibit invalid types from being used as \ 
atomics.
* Improved internal lock pool implementation. The pool is larger, and lock \ 
selection accounts for atomic object alignment, which should reduce the \ 
potential of thread contention.
* Fixed incorrect x86 code generated for bit_test_and_* operations on 8 and \ 
16-bit arguments. Other architectures are not affected.
* Fixed a possible unaligned memory access in compare_exchange_* operations, if \ 
alignment requirements of value_type are less than that of the internal storage \ 
of atomic.
* boost/atomic/atomic.hpp no longer includes boost/atomic/atomic_flag.hpp and \ 
boost/atomic/fences.hpp and only defines the boost::atomic class template and \ 
related typedefs. Include the other headers explicitly or use boost/atomic.hpp \ 
to include all parts of Boost.Atomic.
* The atomic<T>::storage() accessor and associated \ 
atomic<T>::storage_type type are deprecated. Instead, users are advised to \ 
use atomic<T>::value() and atomic<T>::value_type, respectively. \ 
Users can define BOOST_ATOMIC_SILENCE_STORAGE_DEPRECATION to disable deprecation \ 
warnings for the time of transition. The deprecated pieces will be removed in a \ 
future release.
* Removed support for BOOST_ATOMIC_DETAIL_HIGHLIGHT_OP_AND_TEST. This macro was \ 
used as a helper for transition to the updated returned values of *_and_test \ 
operations in Boost.Atomic 1.67, which was released 2 years before 1.73.
Beast:
* This is a maintenance update.
* Nested mutable_data_type in Beast dynamic buffers is deprecated.
* We'd love to know how you or your company use Beast, consider adding an entry \ 
to the Companies and Individuals Using Beast list.
* See the full Release Notes for a complete list of changes.
Context:
* IBM Z: Fix fcontext routines
* mips64/n64: .align 3
* Use OSPLAT MIPS32/MIPS64 to set different ABI
* Fix non-PIC in RISC-V assembly
Conversion:
* Added boost::polymorphic_downcast for references (thanks to Julien Delacroix \ 
for the patch).
* Significant docs update.
date_time:
* Support constexpr in c++14 and above
* Make date_time all inline. Users no longer need to link the library for any \ 
functions. Library remains for build compatibility.
* Deprecate support for legacy io and USE_DATE_TIME_PRE_1_33_FACET_IO macro
* Misc documentation updates and bugfixes.
DLL:
* Fixes and tests for demangling in boost::dll::smart_library
* Make UB sanitizers happy with boost::dll::load_mode::type
* Ceased dependence on MPL improving compile times
* Clang and ICC on Windows fixes and CI support for those platforms
* Maintenance work, including CI hardening and tests improving.
Dynamic Bitset:
* Fixed a portability issue in the definition of the maximum block limit.
Flyweight:
* Maintenance work.
Geometry:
* Improvements
  - Missing input combinations in intersection() and introduction of tupled-output.
  - Added d3::point_xyz geometry model (thanks to Digvijay Janartha).
* Solved issues
  - Incorrect definition of EPSG:3785.
* Bugfixes
  - R-tree exception-safety improvement.
  - Andoyer inverse formula fixed for close points.
  - Fixed dangling reference in distance algorithm.
* Deprecation
  - Support for C++03 has been deprecated and Geometry will require C++14 from \ 
Boost 1.75 onwards.
GIL:
* Added move constructor and move assignment operator to image class
* New member function size() in any_image_view class
* Replace Boost.Test with Boost.LightweightTest as the only test framework used \ 
in GIL. This also restructured the test/extension/io/ sub-tree and targets in \ 
related Jamfile-s.
* Removed remaining uses of Boost.MPL
* Renamed all macros using BOOST_GIL_ prefix
* Renamed all CMake configuration options using BOOST_GIL_ prefix
* Removed extension/dynamic_image/reduce.hpp as unused and possibly unfinished. \ 
An implementation attempt of techniques described in the paper Efficient \ 
Run-Time Dispatching in Generic Programming with Minimal Code Bloat by Lubomir \ 
Bourdev, Jaakko Jarvi.
* Removed direct dependency on Boost.MPL, Boost.System and Boost.Test.
* Started removing public macros for compile-time configuration of I/O extension \ 
tests, i.e. BOOST_GIL_IO_TEST_ALLOW_READING_IMAGES and \ 
BOOST_GIL_IO_TEST_ALLOW_WRITING_IMAGES. Instead, if a test target is built, it \ 
builds all its test cases unconditionally.
* Avoid longjmp interaction during destruction of I/O extension objects.
* Fixed missing alignment default value in constructor of image class.
* Fixed segmentation fault when reading corrupted PNG file.
* Fixed illegal initialization of return values in the old IOv1 interface of I/O \ 
extension.
Histogram:
* Added crop command to reduce algorithm
* slice command in reduce now works on category axis
* Added count accumulator, can be used to add arbitrary metadata to each cell
* sum algorithm gained a new argument to optionally sum only over inner bins
* Several fixes for bugs in corner cases
* Enhanced documentation
icl:
* Remove references to date_time compiled library.
* Fix forward decl lower and upper less equal.
* Misc bugfixes.
IO:
* Made all the IOS state saver classes non-copyable. (Glen Fernandes)
* Correctly handle error upon first read from the input stream when reading a \ 
quoted string. (Glen Fernandes)
* Implemented ostream_joiner for delimiter based joining. (Glen Fernandes)
* Relocated ostream_string from the Utility library to the IO library as ostream_put.
* Correctly handle stream width and fill in quoted output. (Glen Fernandes)
* Optimize quoted output to write directly to the stream buffer. (Glen Fernandes)
* Glen Fernandes became the maintainer of the IO library.
LexicalCast:
* Maintenance work, including CI hardening and better workarounds for broken \ 
standard libraries
Log:
* Default sink used in trivial logging, when no sinks are registered in the \ 
logging core, now automatically flushes output after each log record
* core::flush now performs a flush on the default sink used for trivial logging, \ 
when no sinks are registered.
* Added a workaround for some syslog API implementations (e.g. glibc), which do \ 
not save the application identification string in openlog call. Such \ 
implementations could access already freed memory on each syslog call, resulting \ 
in undefined behavior.
* Fixed that log file rotation on a specific day of month (e.g. \ 
rotation_at_time_point(boost::gregorian::greg_day(1))) could be silently ignored \ 
and not happen.
* Fixed that text_file_backend::rotate_file could throw if there were no log \ 
records written yet and target file name pattern was set.
* Ported various components of the library to std::allocator_traits to improve \ 
compatibility with C++20 allocators.
* Fixed compilation errors when building in MSYS2 Cygwin environment.
Math:
IMPORTANT: C++03 support is now deprecated and will be removed from March 2021.
* Added Cubic Hermite Interpolation.
* Added Modified Akima Interpolation.
* Added PCHIP Interpolation.
* Added Quintic Hermite Interpolation.
* Added entropy to numerous distributions.
* Allow trivial quadrature case where the two end points are equal, and in \ 
addition allow bounds to be interchanged.
* Fix exp_sinh quadrature to work with complex types over a non-native range.
* Fix miscellaneous compiler warnings in factorial.hpp.
* Use std::chrono rather than boost::chrono in timed pFq calculations.
* Remove much of the old boost::mpl dependencies to improve constexpr support.
Mp11:
* Added mp_unique_if (contributed by Kris Jusiak)
* Added mp_flatten
* Added mp_rotate_left, mp_rotate_right (contributed by Duncan Barber)
* Added mp_compose
* Added mp_power_set
* Added mp_partial_sum
* Added mp_iterate
Multi-index Containers:
* multi_index_container is now AllocatorAware.
* Swapping of internal KeyFromValue, Compare, Hash and Pred objects now selects \ 
the appropriate swap function between std::swap and ADL candidates, in \ 
accordance with standard specifications in [swappable.requirements]
* Provided some internal copy constructors and assignment operators whose \ 
default implicit definition is deprecated in C++11 onwards ([depr.impldec]), \ 
which was warned about on some compilers.
Multiprecision:
* IMPORTANT: Mark C++03 support as deprecated and due for removal in 2021.
* Big update to cpp_int adds faster Karatsuba and Coomba multiplication routines.
* Fix conversion of gmp_rational to long double and __float128
* Fix up libtommath support to function with the latest libtom releases.
* Fix up some incompatibilities with the latest Intel C++ compiler.
* Fix up constexpr arithmetic support for latest MSVC release.
Outcome:
* Performance of Outcome-based code compiled by clang has been greatly improved. \ 
The previous implementation of Outcome's status bitfield confused clang's \ 
optimiser, which caused low quality codegen. Unlike most codegen issues, this \ 
was noticeably in empirical benchmarks of real world code, as was shown by P1886 \ 
Error speed benchmarking.
* The safe part of the better_optimisation Outcome v2.2.0 future branch was \ 
merged to Outcome v2.1.3 which includes a new status bitfield implementation. \ 
This appears to not confuse clang's optimiser, and clang 9 produces code which \ 
routinely beats GCC 9's code for various canned use cases.
* Installability is now CI tested per commit. Due to installability of \ 
standalone Outcome (e.g. make install) breaking itself rather more frequently \ 
than is ideal, installability is now tested on CI per commit.
* Newer Concepts implementing compilers were unhappy with the early check for \ 
destructibility of T and E, so removed template constraints, falling back to \ 
static assert which runs later in the type instantiation sequence.
* A false positive undefined behaviour sanitiser failure in some use cases of \ 
Experimental Outcome was worked around to avoid the failure message.
PolyCollection:
* Suppressed a potential redundant move warning in boost::poly_collection::for_each.
* Fixed a bug by which elements were copied rather than moved in \ 
allocator-extended move construction and move assigment between collections with \ 
non-propagating, unequal allocators.
* Allocator-extended move construction no longer decays to allocator-extended \ 
copy construction for the legacy version of libstdc++-v3 shipped with GCC 4.8 \ 
(which can also be used by Clang).
Stacktrace:
* Added documentation on distribution of PDBs
* Fixed msvc-9 build
* Maintenance work, including test fixes fixing typos CI improvements and \ 
hardening, inspect tool fixes.
Test:
* Boost.test v3.13 see the Changes log for more details.
* New feature: It is now possible to combine tolerance indication, user message \ 
and collection comparison modifier in a single BOOST_TEST expression. See change \ 
logs for more details.
ThrowException:
* Added an overload of throw_exception that takes a boost::source_location object.
* NOTE: Projects using BOOST_THROW_EXCEPTION with exceptions disabled will need \ 
to add a definition of this new overload.
TTI:
* Added introspection of function templates for more recent C++ compilers \ 
versions from gcc and vc++. as well as all versions of clang. Older versions of \ 
vc++ before 14.0 and gcc prior to 4.8 may fail.
* Added specific introspection for elements of struct/class, enum, and union \ 
types, which can be used for more fine-grained introspection than the general \ 
'type' introspection.
TypeIndex:
* Maintenance work, including CI integration with inspect tool.
Utility:
* The ostream_string facility has moved from the Utility library to the IO \ 
library as ostream_put.
Variant:
* Removed unused includes
* Fixed zero-as-null-pointer-constat warnings
* Maintenance work, including typo fixes.
Variant2:
* Added support for std::hash, boost::hash.
* variant<T...> is now trivial when all types in T... are trivial. This \ 
improves performance by enabling it to be passed to, and returned from, \ 
functions in registers.
WinAPI:
* Headers in boost/detail/winapi are deprecated and will be removed in a future \ 
release.
* Boost.WinAPI headers no longer include winerror.h. Include \ 
boost/winapi/error_codes.hpp to get Windows error codes.

Log message:
boost: updated to 1.72.0

Version 1.72.0

Asio:
Changed the async_initiate helper function to automatically deduce its return \ 
type, for C++11 or later.
Changed all asynchronous operations to use automatically deduced return types, \ 
for C++14 or later.
Introduced concepts to support async_initiate.
Added the nested template type rebind_executor to all I/O object types.
Changed the initiation function objects to report their associated I/O executor \ 
via the nested type executor_type and member function get_executor().
Added the default_completion_token trait, giving I/O executor types an \ 
associated default completion token type for use with asynchronous operations. \ 
This trait is specialised for the use_awaitable completion token, for example, \ 
to allow asynchronous operations to be used as follows: co_await \ 
socket.async_connect(my_endpoint).
Added missing async_initiate to the Windows-specific I/O objects' asynchronous \ 
operations.
Ensured that the executor type is propagated to newly accepted sockets.
Changed to require that Protocol copy and move operations never throw.
Changed to require that Endpoint default constructor and move operations never throw.
Added the noexcept qualifier to protocol accessors.
Added the noexcept qualifier to socket move constructors.
Fixed issues associated with opening serial ports on Windows:
Use the correct constant to initialise the RTS control flag.
Specify a default baud rate (9600).
Fixed a lost "outstanding work count" that can occur when an \ 
asynchronous accept operation is automatically restarted.
Consult the Revision History for further details.

Atomic:
Added a workaround for __float128 not being considered as a floating point type \ 
by some versions of libstdc++.
Improved compatibility with clang-win compiler.

Beast:
This is a maintenance update containing bug fixes, and updates to use the new \ 
features delivered in Boost.Asio.
We'd love to know how you or your company use Beast, consider adding an entry to \ 
the Companies and Individuals Using Beast list.
See the full Release Notes for a complete list of changes.

Circular Buffer:
Fix: max_size() now takes the allocator's max_size() into account. (Glen Fernandes)

Context:
architecture s390x supported
execution_context removed

Endian:
Made endian_reverse, conditional_reverse and *_to_* constexpr on GCC and Clang
Added convenience load and store functions
Added floating point convenience typedefs
Added a non-const overload of data(); changed its return type to unsigned char*
Added __int128 support to endian_reverse when available
Added a convenience header boost/endian.hpp

Filesystem:
Extracted filesystem_error to exception.hpp; file_status and associated enums \ 
and functions to file_status.hpp; directory_entry, directory_iterator and \ 
recursive_directory_iterator to directory.hpp.
Deprecated: For backward compatibility operations.hpp still includes the new \ 
headers exception.hpp, file_status.hpp and directory.hpp, unless \ 
BOOST_FILESYSTEM_NO_DEPRECATED macro is defined. These implicit includes are \ 
considered deprecated and will be removed in a future release. Users are \ 
encouraged to include the new headers directly or include filesystem.hpp.
The filesystem_error exception is now implemented in the compiled library of \ 
Boost.Filesystem. Users may need to add linking with Boost.Filesystem library in \ 
their projects.
On POSIX.1-2008 platforms, use utimensat instead of utime. utime is declared \ 
obsolete in POSIX.1-2008 and can be disabled e.g. in uClibc-ng.
directory_iterator is now left in the end state on memory allocation errors.
In directory_iterator on POSIX systems, support for readdir/readdir_r has been \ 
reworked to avoid memory allocations for dirent structures when readdir is used. \ 
This reduces memory consumption and eliminates the possibility of buffer \ 
overruns in case if readdir produces a very long directory name.
On Windows, use Boost.WinAPI to select the target Windows version.
New: Added directory_options enum, which reflects the same named enum from \ 
C++20. The enum is supported in directory_iterator and \ 
recursive_directory_iterator to customize iteration behavior. In particular, the \ 
iterators now support skipping directories that can't be opened due to \ 
insufficient permissions. The symlink_option enum is now deprecated and should \ 
be replaced with directory_options.
By default, recursive_directory_iterator is now reset to the end state in case \ 
of errors, as required by C++20.
New: Added directory_options::pop_on_error option, which configures \ 
recursive_directory_iterator so that it attempts to recover from iteration \ 
errors by repeatedly invoking pop() until it succeeds or the end state is \ 
reached.
New: Added directory_options::skip_dangling_symlinks option, which configures \ 
recursive_directory_iterator so that it doesn't follow dangling directory \ 
symlinks and continues iteration instead of reporting an error.
Deprecated: The following members of recursive_directory_iterator are now marked \ 
as deprecated: level(), no_push_pending(), no_push_request(), no_push(). Users \ 
are advised to replace their use with the standard counterparts: depth(), \ 
recursion_pending(), disable_recursion_pending(). Note that recursion_pending() \ 
has the opposite meaning compared to no_push_pending() and no_push_request(). \ 
Deprecated methods will be removed in a future release.
Fixed path::lexically_relative (and any dependent algorithms) to correctly \ 
handle empty, dot and dot-dot path elements in its argument. The behavior is \ 
made closer to C++17 std::path::lexically_relative in that empty and dot path \ 
elements are ignored and dot-dot path elements are accounted by decreasing the \ 
number of dot-dot path elements to generate in the resulting relative path.

Functional/Factory:
Glen Fernandes rewrote the implementations of factory and value_factory to \ 
provide the following features:
Support r-value arguments when possible
Support arbitrary number of arguments via variadic templates when possible
Support allocators that are final
Support allocators that use fancy pointers
Support for disabled exceptions (BOOST_NO_EXCEPTIONS)
Improved compilation times
The following features have been removed:
Increasing limits for C++03 compilers through \ 
BOOST_FUNCTIONAL_VALUE_FACTORY_MAX_ARITY
Using boost::none_t in place of void through BOOST_FUNCTIONAL_FACTORY_SUPPORT_NONE_T

GIL:
Added
GSoC 2019: Lanczos resampling for image down scaling.
GSoC 2019: Methods for binary thresholding, inverted binary thresholding and \ 
truncation thresholding.
GSoC 2019: Otsu thresholding method.
GSoC 2019: Adaptive thresholding using mean or gaussian-weighted sum of the \ 
neighbourhood area.
GSoC 2019: Harris response calculation (corner detector without non-maximum \ 
filtering).
GSoC 2019: Hessian corner detector.
GSoC 2019: Types for defining 2D kernel, kernel_2d and kernel_2d_fixed, in \ 
Numeric extension.
GSoC 2019: Implementation of 2D convolution as new function convolve_2d.
GSoC 2019: Box filtering using the average filter.
GSoC 2019: Blur function based on normalized mean filter.
GSoC 2019: Sobel and Scharr operators.
GSoC 2019: Median filter to remove noise from image.
Continued adding new test cases and significantly improved overall test coverage.
Documented purpose of cached_location_t.
Function convolve_1d in Numeric extension for convenient use of convolve_rows \ 
and convolve_cols.
Function extend_boundary in Numeric extension to perform image boundary extension.
Project release notes maintained in Markdown file RELEASES.md.

Changed
Move all tests, core features and extensions, inside test/ directory.

Removed
Replace Boost.MPL with Boost.MP11.
Removed use of Boost.TypeTraits.
Dropped support for GCC <= 4.8.
Remove include/boost/gil/version.hpp file as unused.

Fixed
Undetermined value of default-initialized channel and pixel objects.
Undefined behaviour due to std::is_trivially_default_constructible specializations.
Crash when reading PNG files with an invalid header.
Applied the Rule of Three for numerous types.
Removed uses of deprecated implicit definition of defaulted copy assignment \ 
operator or copy constructor.

Histogram:
Several new features and performance improvements, some bug-fixes
See the full Release Notes for a complete list of changes

Log:
Improved compatibility with clang-win compiler.

MPI:
Documentation clarifications.
Fixed scatterv bug when using explicit input buffer offsets.
Enable usage of MPI_Probe and friend with Intel MPI >= 2019.4
Symbol visibility on Windows

Math:
Added Hypergeometric functions 1F0, 0F1, 2F0, 1F1 and pFq.
Added Jacobi polynomial (and derivatives) evaluation.
Added Gegenbauer polynomial (and derivatives) evaluation.
Added Cardinal B-Splines (and derivatives) as polynomial functions in their own \ 
right.
Added Cardinal Trigonometric Interpolation.
Added new statistics sub-section.
Added One Sample Student's T Test.
Added Anderson Darling test for normality.
Added Ljung Box test for auto-correlation.
Added Runs test for random sequences.
The headers boost/math/tools/univariate_statistics.hpp and \ 
boost/math/tools/bivariate_statistics.hpp, have been deprecated in favor of \ 
boost/math/statistics/univariate_statistics.hpp and \ 
boost/math/statistics/bivariate_statistics.hpp.
Added The Empirical CDF distribution.
Reworked the Sterling approximation used by multiprecision gamma functions to be \ 
applicable to all the function that use the Lanczos approximation at regular \ 
precision. Also extended Lanczos approximations up to 100 decimal digit \ 
precision.

Multiprecision:
Big constexpr update allows cpp_int and float128 arithmetic to be fully \ 
constexpr with gcc and clang 9 or later, or any compiler supporting \ 
std::is_constant_evaluated().
Fix bug in variable precision mpf_float which causes it to go into a tailspin \ 
trying to select the correct precision - see \ 
https://github.com/boostorg/multiprecision/issues/164.

Outcome:
Enhancements:
Standalone outcome is now make install-able, and cmake find_package() can find \ 
it. Note that you must separately install and find_package() Outcome's \ 
dependency, quickcpplib, else find_package() of Outcome will fail.
The git submodule mechanism used by standalone Outcome of specifying dependent \ 
libraries has been replaced with a cmake superbuild of dependencies mechanism \ 
instead. Upon cmake configure, an internal copy of quickcpplib will be git \ 
cloned, built and installed into the build directory from where an internal \ 
find_package() uses it. This breaks the use of the unconfigured Outcome repo as \ 
an implementation of Outcome, one must now do one of: 1. Add Outcome as \ 
subdirectory to cmake build. 2. Use cmake superbuild (i.e. \ 
ExternalProject_Add()) to build and install Outcome into a local installation. \ 
3. Use one of the single header editions.
For standalone Outcome, the current compiler is now checked for whether it will \ 
compile code containing C++ Concepts, and if it does, all cmake consumers of \ 
Outcome will enable C++ Concepts. Set the cmake variable CXX_CONCEPTS_FLAGS to \ 
an empty string to prevent auto detection and enabling of C++ Concepts support \ 
occurring.
OUTCOME_TRY operation now hints to the compiler that operation will be \ 
successful. [P1886 Error speed benchmarking](https://wg21.link/P1886) showed \ 
that there is considerable gain in very small functions by hinting to the \ 
compiler whether the expression is expected to be successful or not. OUTCOME_TRY \ 
previously did not hint to the compiler at all, but now it does. A new suite of \ 
macros OUTCOME_TRY_FAILURE_LIKELY hint to the compiler that failure is expected. \ 
If you wish to return to the previously unhinted behaviour, define \ 
OUTCOME_TRY_LIKELY(expr) to (!!expr).
Support for C++ Coroutines has been added. This comes in two parts, firstly \ 
there is now an OUTCOME_CO_TRY() operation suitable for performing the TRY \ 
operation from within a C++ Coroutine. Secondly, in the header \ 
outcome/coroutine_support.hpp there are implementations of \ 
eager<OutcomeType> and lazy<OutcomeType> which let you more \ 
naturally and efficiently use basic_result or basic_outcome from within C++ \ 
Coroutines -- specifically, if the result or outcome will construct from an \ 
exception pointer, exceptions thrown in the coroutine return an errored or \ 
excepted result with the thrown exception instead of throwing the exception \ 
through the coroutine machinery (which in current compilers, has a high \ 
likelihood of blowing up the program). Both eager<T> and lazy<T> can \ 
accept any T as well. Both have been tested and found working on VS2019 and \ 
clang 9.
make_error_code() and make_exception_ptr() are now additionally considered for \ 
compatible copy and move conversions for basic_result<>. This lets you \ 
construct a basic_result<T, E> into a basic_result<T, error_code>, \ 
where E is a custom type which has implemented the ADL discovered free function \ 
error_code make_error_code(E), but is otherwise unrelated to error_code. The \ 
same availability applies for exception_ptr with make_exception_ptr() being the \ 
ADL discovered free function. basic_outcome<> has less support for this \ 
than basic_result<> in order to keep constructor count down, but it will \ 
accept via this mechanism conversions from basic_result<> and \ 
failure_type<>.

Bug fixes:
The detection of [[nodiscard]] support in the compiler was very mildly broken.

PolyCollection:
Maintenance work.

Preprocessor:
Topic added which discusses emptiness
Support for the C++20 __VA_OPT__ construct
BOOST_PP_VARIADIC_HAS_OPT whether __VA_OPT__ is supported at the C++20 level
BOOST_PP_CHECK_EMPTY test for emptiness using __VA_OPT__ at the C++20 level
BOOST_PP_VA_OPT more flexible alternative to __VA_OPT__ at the C++20 level

Smart Pointers:
Implemented allocate_unique for scalars and arrays. (Glen Fernandes)

Test:
Boost.test v3.12 see the Changes log for more details.
New feature:
Support for C++17 std::string_view has been added.
Better diagnostic on boost::exception and no rtti mode (thanks to Mikhail Pilin \ 
/ [pull_request 234])

VMD:
BOOST_VMD_IS_EMPTY updated to use __VA_OPT__ at the C++20 level has 100% reliability

Log message:
Fix devel/boost-libs build under recent NetBSD 9.99

* Follow EV_SET fingerprint change
* Bump PKGREVISION of devel/boost-headers

Log message:
Bump PKGREVISION because the file has been changed.

Log message:
Fix "include/boost/core/uncaught_exceptions.hpp.orig" missing from PLIST
by removing *.orig files at the start of do-install. Remove *.orig from
PLIST to match.

Log message:
Update to 1.71.0

Changelog:

New Libraries

    Variant2: A never-valueless, strong guarantee implementation of \ 
std::variant, from Peter Dimov.

Updated Libraries

    Align:
        Support for any integral type in the integral versions of align_up and \ 
align_down.
        Revised the implementation of aligned_allocator to no longer require a \ 
specialization for void.
        Define propagate_on_container_move_assignment and is_always_equal in \ 
aligned_allocator.
    Asio:
        Improved performance slightly by eliminating a redundant move \ 
construction when completed handlers are dispatched.
        Eliminated a compiler warning by annotating a case fall-through in the \ 
free function connect() implementation.
        Fixed the is_*_buffer_sequence detection traits for user-defined \ 
sequence types.
        Fixed some Windows-specific warnings about an incompatible pointer cast \ 
when obtaining the CancelIoEx entry point.
        Changed to automatically set the defaults when opening a serial port on \ 
Windows.
        Changed the serial port get_option() member function to be const.
        Fixed a name hiding issue with the WinRT stream-oriented socket \ 
backend's shutdown function.
        Applied a minor fix to the documentation for is_dynamic_buffer.
        Added some support for Haiku OS.
        Added wolfSSL compatability.
        Changed to require C++17 or later for coroutines TS support with clang.
        Fixed a doxygen generation problem in the tutorial.
        Ensured example programs are correctly incorporated into the documentation.
    Any:
        Static initialization of the default constructed boost::any is now possible.
        Fixed performance regression in assignment on a compilers without \ 
move-semantics.
        Maintenance work.
    Beast:
        This version consists mostly of bug fixes and performance improvements.
        Substantial work included for the split compilation mode, to reduce \ 
compile time when defining BOOST_BEAST_SEPARATE_COMPILATION.
        We'd love to know how you or your company use Beast, consider adding an \ 
item to the Companies and Individuals Using Beast list.
        See the full Release Notes for a complete list of changes.
    Circular Buffer:
        Correct doxygen generated reference to no longer show internal members. \ 
(Glen Fernandes)
        Eliminate ubsan warning on add and sub. (Glen Fernandes)
        Fix incorrect check in is_uninitialized. (Niklas Fejes)
    Container:
        Fixed bugs:
            GitHub #47: "added alignment specification for small_vector".
            GitHub #88: "Implement C++17 MoveAssignable requirements for \ 
self-move assignments".
            GitHub #107: "Alignment ignored in resource_adaptor".
            GitHub #109: "Get rid of integer overflow in copy_move_algo.hpp \ 
(-fsanitize=integer)".
            GitHub #110: "Avoid gcc 9 deprecated copy warnings in \ 
new_allocator.hpp".
            GitHub #112: "vector::resize() compilation error with \ 
msvc-10..12: data is not a member of boost::detail::aligned_storage".
            GitHub #114: "Fix small_vector noexcept specification".
            GitHub #116: "MSVC + boost 1.70 compilation error when \ 
windows.h is already included (detail/thread_mutex.hpp)".
            GitHub #117: "flat_map/map::insert_or_assign with hint has \ 
wrong return types".
            GitHub #118: "Non-unique inplace_set_difference used in in \ 
flat_tree_merge_unique and iterator invalidation in insert_unique".
            GitHub #122: "Fix has_trivial_destructor_after_move".
            GitHub #123: "With heterogeneous lookup, equal_range can result \ 
in a range with length greater than 1".
        deque can now have options, using deque_options. The block size/bytes \ 
can be be specified.
        static_vector can now have options, using static_vector_options. \ 
Alignment and throwing behaviour can be be specified.
        small_vector can now have options, using small_vector_options. Alignment \ 
and growth factor can be be specified.
    Context:
        Add support for RISC-V LP64D
        #72: Fix ABI violation on ppc64 ELFv2
        #99: cleanup of stack if creating ucontext fails
    Conversion:
        Maintenance work.
    Core:
        Added functions alloc_construct, alloc_construct_n, alloc_destroy, and \ 
alloc_destroy_n in <boost/core/alloc_construct.hpp> for allocator aware \ 
and exception safe construction and destruction of objects and arrays. (Glen \ 
Fernandes)
        Added constexpr functions first_scalar in \ 
<boost/core/first_scalar.hpp> for obtaining a pointer to the first scalar \ 
element of an array. Given a pointer of type T* they return a pointer of type \ 
remove_all_extents_t<T>*. (Glen Fernandes)
        Added class template noinit_adaptor in \ 
<boost/core/noinit_adaptor.hpp> which is an allocator adaptor that \ 
converts any allocator into one whose construct(ptr) performs default \ 
initialization via placement new, and whose destroy(ptr) invokes the value_type \ 
destructor directly. (Glen Fernandes)
        Added class template default_allocator in \ 
<boost/core/default_allocator.hpp>, which can serve as a minimal default \ 
allocator that has interface similar to C++20 std::allocator, supports \ 
configurations with disabled exceptions and does not have std as an associated \ 
namespace. The allocator uses operator new and operator delete for allocation. \ 
(Glen Fernandes)
        In <boost/core/uncaught_exceptions.hpp> header, added workarounds \ 
for better compatibility with QNX SDP 7.0 when libc++/libc++abi libraries are \ 
used. (Andrey Semashev, #59)
        The <boost/detail/sp_typeinfo.hpp> header is now marked as \ 
deprecated and will be removed in a future release. \ 
<boost/core/typeinfo.hpp> should be used instead. (Peter Dimov)
    Dynamic Bitset:
        Enabled hardware-assisted popcount on MSVC (#38).
        Added support for boost::hash and std::hash (#45).
        Support copy-initialization with default constructor (#48).
    Endian:
        Clarified requirements on the value type template parameter
        Added support for float and double
        Added endian_load, endian_store
        Updated endian_reverse to correctly support all non-bool integral types
        Moved deprecated names to the deprecated header endian.hpp
    Fiber:
        documentation for shared_work updated
    Filesystem:
        Fixed incorrect error_code returned from directory iterator increment \ 
when readdir_r is used.
        For path, fixed rvalue-aware operator/ return type to return an rvalue \ 
instead of rvalue reference. This fixes leaving a dangling reference in the \ 
user's code if the result of operator/ is bound to a const reference. (#110)
        Fixes for better compatibility with Windows CE. (#24)
        Added minimal support for CMake. (#106)
    Flyweight:
        Maintenance work.
    Histogram:
        New features:
            Support for thread-safe storages and new thread-safe accumulators
            Support for compiling without exceptions/RTTI (increases performance \ 
by 10-20 %) (with Glen Fernandes)
            Performance improvements for 1D and 2D histograms
            boost::histogram::indexed now returns forward iterator range instead \ 
of input iterator range
            boost::histogram::indexed_range::accessor is now non-copyable and \ 
acts like reference to cell value, making more algorithms from the C++ stdlib \ 
work
            boost::histogram::algorithm::reduce with new slice option and option \ 
fusion
            boost::histogram::algorithm::project accepts runtime indices for \ 
static histograms
        Bug Fixes:
            boost::histogram::algorithm::reduce also works on histograms that \ 
have some axis types without reduction support
            boost::histogram::axis::traits::update now works correctly for \ 
boost::histogram::axis::variant
        Other:
            100 % test coverage
            Reduced internal Boost dependencies
            Improved documentation and examples
            Guaranteed no-throw moves for all builtin axis types
            Compile cleanly at higher warning levels
        See changelog for more details.
    IoStreams:
        Fixed processing of multi-stream files (#87).
        Added support for multi-threaded LZMA (#95).
    Interprocess:
        GitHub #85 ("warning: Implicit conversion loses integer \ 
precision").
        GitHub #86 ("warning: Possible misuse of comma operator").
    Intrusive:
        GitHub #42: Documentation does not describe treap priority_of_value changes
        GitHub #43: Fix tests with BOOST_INTRUSIVE_VARIADIC_TEMPLATES enabled
        GitHub #45: Disable variadic templates for MSVC-12 to avoid ICEs
    LexicalCast:
        Added tests for boost::filesystem::path conversions #25.
        Maintenance work, including #28.
    Log:
        New features:
            Improved support for C++17 std::string_view in \ 
basic_formatting_ostream. The string view can now participate in character code \ 
conversion on output.
            Added auto_newline formatter and stream manipulator. It can be used \ 
to ensure that formatted output always ends with a newline while avoiding \ 
duplicate newlines.
            In the output stream, text file and text multi-file sink backends \ 
added support for configuring behavior with regard to appending a trailing \ 
newline to every formatted log record. Use auto_newline_mode named parameter of \ 
the backend constructor or call the set_auto_newline_mode method on the sink \ 
backend.
            Note: The default behavior with regard to trailing newlines added by \ 
sink backends has changed slightly compared to the previous Boost.Log releases. \ 
The backends will now only add a trailing newline if there isn't one in the \ 
formatted log message string already. In previous releases a newline was added \ 
unconditionally.
            Added support for passing arbitrary function objects in the filter \ 
and format named parameters to sink constructors and convenience functions for \ 
initializing sinks. For example, it is now possible to specify C++11 lambda \ 
functions directly in these parameters. (#63)
            In the default filter and formatter factories used in filter and \ 
formatter parsers, added support for severity level attribute values of type \ 
boost::log::trivial::severity_level. For filters, the support is limited to \ 
attributes with "Severity" name.
        Bug fixes:
            Fixed incorrect parsing of components of the rotated file names \ 
while scanning for files in the text file sink backend. If the file name pattern \ 
ended with a placeholder (for example, a file counter), the scan_for_files \ 
method would not find files matching that pattern in the target storage, leaving \ 
them unmanaged. In particular, such files would not be deleted to free target \ 
storage. (#78)
            Updated basic_formatting_ostream and basic_record_ostream to make it \ 
possible to overload stream output operators for pointers to user-defined types. \ 
User-defined operator<< overloads taking std::basic_ostream and a pointer \ 
argument should now be picked up by the compiler when the pointer is being \ 
written to one of Boost.Log streams. (#84)
        See changelog for more details.
    Math:
        New features:
            Catmull-Rom interpolator now works in C++11
            Cardinal quadratic B-spline interpolation
            Domain of elliptic integrals extended
            sin_pi and cos_pi performance improvements
            Forward-mode automatic differentiation
            Vector valued barycentric rational interpolation
            Ooura's method for evaluation of Fourier integrals
        Bug fixes:
            Multiple compatibility issues with Multiprecision fixed
            Lambert-W fixed on a rare architecture
    Metaparse:
        New features:
            In C++11 variadic template support for the following: sequence, \ 
one_of_c, one_of, repeated_one_of, repeated_one_of1, one_char_except_c, \ 
one_char_except.
        Bug fixes:
            BOOST_METAPARSE_STRING does not use out of range character values as \ 
template arguments.
            any_of_c<> does not create empty array in C++14.
    Move:
        Git Issue #26: "Invalid iterator increment/decrement in the last \ 
iteration of adaptive_sort_combine_blocks".
    Multi Array:
        Simplify allocator support by using new alloc_construct_n and \ 
alloc_destroy_n facilities from Core. (Glen Fernandes)
    Multi-index Containers:
        Added variants of const_mem_fun and mem_fun for differently qualified \ 
member functions (issue #24).
        Terse key specification syntax now correctly handles noexcept-specified \ 
member functions (issue #24).
    Outcome:
        Enhancements:
            #184 As per request from Boost release managers, relocated \ 
version.hpp and revision.hpp into detail, and added the Boost licence \ 
boilerplate to the top of every source file which was missing one (I think). \ 
Also took the opportunity to run the licence restamping script over all Outcome, \ 
so copyright dates are now up to date.
            #185 Add FAQ item explaining issue #185, and why we will do nothing \ 
to fix it right now.
            #189 Refactored the OUTCOME_TRY implementation to use more clarified \ 
customisation points capable of accepting very foreign inputs. Removed the \ 
std::experimental::expected<T, E> specialisations, as those are no longer \ 
necessary. Fixed the documentation for the customisation points which previously \ 
claimed that they are ADL discovered, which they are not. Added a recipe \ 
describing how to add in support for foreign input types.
            #183 Added a separate motivation/plug_error_code specifically for Boost.
        Bug fixes:
            OUTCOME_VERSION_MINOR hadn't been updated to 1.
            #181 Fix issue #181 where Outcome didn't actually implement the \ 
strong swap guarantee, despite being documented as doing so.
            #190 Fix issue #190 in Boost edition where unit test suite was not \ 
runnable from the Boost release distro.
            #182 Fix issue #182 where trait::is_exception_ptr_available<T> \ 
was always true, thus causing much weirdness, like not printing diagnostics and \ 
trying to feed everything to make_exception_ptr().
            #192 Fix issue #192 where the \ 
std::basic_outcome_failure_exception_from_error() was being defined twice for \ 
translation units which combine standalone and Boost Outcome's.
    Parameter:
        Upgraded keyword generation macro BOOST_PARAMETER_TEMPLATE_KEYWORD (#15).
        Moved keyword generation macro BOOST_PARAMETER_NESTED_KEYWORD from \ 
Accumulators to this library (#28).
        Added support for std::reference_wrapper and std::ref() (#16).
        Moved boost::parameter::required, boost::parameter::optional, and \ 
boost::parameter::deduced metafunction definitions to their own header files in \ 
directory boost/parameter (#18).
        Added support for Boost.Parameter-enabled function call operators (#20).
        Added support for parameter category qualifiers "forward", \ 
"consume", and "move_from" (current qualifiers are \ 
"in", "out", and "in_out") (#21) (#23) based on \ 
http://www.modernescpp.com/index.php/c-core-guidelines-how-to-pass-function-parameters. \ 
Added new usage syntax BOOST_PARAMETER_NAME((object-name), namespace-name) \ 
qualifier(tag-name)) and BOOST_PARAMETER_NAME(qualifier(name)). (Existing code \ 
that uses qualifiers directly and correctly with BOOST_PARAMETER_FUNCTION and \ 
other code generation macros should remain unaffected for now, so no breaking \ 
changes.) The reason for the change in usage is to enable applying of parameter \ 
category constraints to Boost.Parameter-enabled functions and constructors \ 
invoked through argument composition. (Otherwise, it is currently possible to \ 
use argument composition to bypass parameter category constraints applied in \ 
BOOST_PARAMETER_FUNCTION et. al.)
        Added support for perfect forwarding (#23) (#26), so that \ 
parameter::parameters::operator() can accept non-const rvalues. As a positive \ 
side effect, Boost.Parameter-enabled functions and constructors are no longer \ 
bound by BOOST_PARAMETER_MAX_ARITY on compilers that support perfect forwarding. \ 
User code can now check for this support by detecting the configuration macro \ 
BOOST_PARAMETER_HAS_PERFECT_FORWARDING, or manually turn off this support by \ 
defining the configuration macro BOOST_PARAMETER_DISABLE_PERFECT_FORWARDING.
        Added metafunctions boost::parameter::is_argument_pack (#27), \ 
boost::parameter::are_tagged_arguments (#52), and \ 
boost::parameter::result_of::compose (#75).
        Added variadic function template boost::parameter::compose() which takes \ 
in named arguments and returns them in an argument pack (#52). For compilers \ 
that do not support perfect forwarding, the configuration macro \ 
BOOST_PARAMETER_COMPOSE_MAX_ARITY determines the maximum number of arguments \ 
that boost::parameter::compose() can take in (#61).
        Added code generation macros \ 
BOOST_PARAMETER_BASIC_FUNCTION_CALL_OPERATOR, \ 
BOOST_PARAMETER_BASIC_CONST_FUNCTION_CALL_OPERATOR, \ 
BOOST_PARAMETER_NO_SPEC_FUNCTION, BOOST_PARAMETER_NO_SPEC_MEMBER_FUNCTION, \ 
BOOST_PARAMETER_NO_SPEC_CONST_MEMBER_FUNCTION, \ 
BOOST_PARAMETER_NO_SPEC_FUNCTION_CALL_OPERATOR, \ 
BOOST_PARAMETER_NO_SPEC_CONST_FUNCTION_CALL_OPERATOR, \ 
BOOST_PARAMETER_NO_SPEC_CONSTRUCTOR, and \ 
BOOST_PARAMETER_NO_SPEC_NO_BASE_CONSTRUCTOR (#52).
        Added support for Boost.MP11 (#47) (#66) (#70). User code can now check \ 
for this support by detecting the configuration macro \ 
BOOST_PARAMETER_CAN_USE_MP11, or manually turn off this support by defining the \ 
configuration macro BOOST_PARAMETER_DISABLE_MP11_USAGE.
        Improved support for parameter-dependent return types via SFINAE (#73).
    PtrContainer:
        Fix a ptr_vector regression introduced in 1.66.0 (#24).
    PolyCollection:
        Maintenance work.
    SmartPtr:
        Added aliasing constructors to weak_ptr
        Added weak_ptr<T>::empty()
        Added enable_shared_from, shared_from, and weak_from
    Stacktrace:
        Fixed output of name(), source_location() and source_line() for the \ 
default constructed frame with thread sanitizer builds in C++98 mode.
        Fixed output of long strings from name() and source_location() on MSVC #78.
        Maintenance work.
    Test:
        Boost.test v3.11 see the Changes log for more details.
        Breaking changes:
            Boost.Test shows deprecation warnings if some very old headers as \ 
deprecated. If you encounter such warnings, please follow the indications: those \ 
headers will be removed in a future release.
        New feature:
            Now BOOST_TEST can be used to compare abstract types
        Bug fixes and pull requests:
            GitHub Issues: #209, #218
            GitHub Pull Requests: #219, #224
    Utility:
        Implemented function template ostream_string in \ 
<boost/utility/ostream_string.hpp> to optimally write any kind of string \ 
content to an output stream. It satisfies the requirements of \ 
[ostream.formatted.reqmts]. (Glen Fernandes)
        Optimized the stream output operators of basic_string_view and \ 
basic_string_ref to write directly to the rdbuf stream buffer. (Glen Fernandes)
    Uuid:
        Breaking change: MD5 name-based uuid generation was corrected to be \ 
identical on all endian systems. Define BOOST_UUID_COMPAT_PRE_1_71_MD5 to keep \ 
the result in a format compatible with 1.66 through 1.70. This does not affect \ 
the default name-based uuid generation which is based on SHA1. (#109)
    Variant:
        Fixed compilation of boost::apply_visitor with variants passed by non \ 
const reference in #68. Many thanks to Ed Catmur for providing the fix.
        Added support for std::hash (#49). Macro \ 
BOOST_VARIANT_DO_NOT_SPECIALIZE_STD_HASH could be defined to avoid those \ 
specializations.
        Added micro optimizations for binary size and performance by Nikita \ 
Kniazev in #63 and #66.
        Maintenance work, including #64 by Nikita Kniazev and #67 by Hans Dembinski.
    YAP:
        Added an example showing how to make self-evaluating YAP expressions \ 
(that is, expressions that don't need an explicit call to evaluate() or \ 
transform()).