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.

    • 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.
    • All I/O objects, asynchronous operations, and utilities will interoperate with both new proposed standard executors, and with existing Networking TS executors.
    • 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.
    • 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:

    • 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.
    • 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.
    • 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

    • PR#720 Additional R-tree constructors (thanks to Caian Benedicto).
    • Various improvements in buffer, set and relational operations.
  • Solved issues

    • #709 memcpy called for object with no trivial copy-assignment.
    • #721 Compilation error in bgi::detail::rtree::visitors::insert.
    • #727 MSVC warning: conditional expression is constant.
  • Bugfixes

    • PR#700 Missing cases for default strategies in distance algorithm.
    • PR#738 Longitudes out of range in direct geodesic formulas.
• GIL:

  • Added

    • Added new constructor initializing any_image from r-value reference to any image (PR#486).
    • Implemented mechanism to reverse kernel_2d (PR#489).
  • Changed

    • 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).
    • Use perfect forwarding from apply_operation to visit (PR#491).
  • Removed

    • BREAKING: Removed dependency on Boost.Variant
  • Fixed

    • Fixed invalid conversion from RGB8 to CMYK32 due to overflow (PR#470).
    • Fixed image constructor from other image (PR#477).
    • Fixed error plane_view_t is not a class or namespace name (PR#481).
    • Fixed interleaved_view factory using point<std::ptrdiff_t> for dimension (PR#487).
    • Fixed documentation replacing uses MPL with MP11 in tutorial (PR#494).
    • Fixed missing header in numeric/kernel.hpp to make it self-contained (PR#502).
  • Acknowledgements

    • 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:

    • 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:

    • Move constructors and assignment operators of various components were marked noexcept.
    • Added a new range_manip stream manipulator that can be used for outputting elements of a range, optionally separated by a delimiter.
    • 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.
    • 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:

    • 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:

    • 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.
    • 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.
    • 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.
    • Concepts now live in OUTCOME_V2_NAMESPACE::concepts namespace. Previously concepts lived in the convert namespace, now they live in their own namespace.
    • 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.
    • 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:

    • #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.
    • 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)

Compilers Tested

Boost's primary test compilers are:

• Linux:

  • Clang: 3.0, 4.0.1, 6.0.1
  • Clang, C++0x: 3.0
  • Clang, C++11: 3.0, 3.1, 3.2, 3.3, 3.4, 4.0.1, 6.0.1, 7.0.0, 8.0.0
  • Clang, C++14: 3.5.0, 3.6.0, 3.7.1, 3.8.0, 3.9.1, 4.0.0, 4.0.1, 5.0.2, 6.0.1, 7.0.0, 8.0.0
  • Clang, C++17: 5.0.2, 6.0.1, 7.0.0, 8.0.0
  • GCC: 4.4.7, 4.5.3, 4.6.3, 5.4.0, 8.0.1
  • GCC, C++0x: 4.4.7
  • GCC, C++11: 4.7.3, 4.8.5, 4.9.4, 5.4.0, 6.4.0, 7.1.0, 8.0.1
  • GCC, C++14: 5.4.0, 5.5.0, 6.4.0, 7.1.0, 7.3.0, 8.0.1
  • GCC, C++17: 7.3.0, 8.0.1
  • Intel, C++14: 18.0
• OS X:

  • Apple Clang: 9.0.0, 9.1.0, 10.0.0
  • Apple Clang, C++11: 9.0.0, 9.1.0, 10.0.0
  • Apple Clang, C++14: 9.0.0, 9.1.0, 10.0.0
  • Apple Clang, C++17: 9.1.0, 10.0.0
  • Apple Clang, C++1z: 9.0.0
  • Apple Clang, C++2a: 10.0.0
• Windows:

  • GCC: 3.4.5, 4.1.2, 4.2.4, 4.3.3, 4.4.0, 4.5.4
  • GCC, C++0x: 4.6.4
  • GCC, C++11: 4.7.3, 4.8.1, 4.9.3
  • GCC, C++14: 5.1.0, 5.2.0, 5.3.0, 6.1.0, 6.2.0, 6.3.0, 6.4.0
  • GCC, C++17: 7.1.0, 7.2.0, 7.3.0
  • Visual C++: 7.1, 8.0, 9.0, 10.0, 11.0, 12.0, 14.0, 14.1
• FreeBSD:

  • Clang: 4.0.0
  • Clang, C++11: 4.0.0
  • Clang, C++14: 4.0.0
  • Clang, C++1z: 4.0.0

Boost's additional test compilers include:

• Linux:

  • Clang: 3.0, 3.8.1, 3.9.1, 4.0.1, 5.0.2, 6.0.1
  • Clang, C++0x: 3.0
  • Clang, C++11: 3.0, 3.1, 3.2, 3.3, 3.4, 4.0.1, 6.0.1, 7.0.0, 8.0.0
  • Clang, C++14: 3.5.0, 3.6.0, 3.7.1, 3.8.0, 3.9.1, 4.0.0, 4.0.1, 5.0.2, 6.0.1, 7.0.0, 8.0.0
  • Clang, C++17: 5.0.2, 6.0.1, 7.0.0, 8.0.0
  • GCC: 4.4.7, 4.5.3, 4.6.3, 4.9.4, 5.4.0, 5.5.0, 8.0.1
  • GCC, C++0x: 4.4.7
  • GCC, C++11: 4.7.3, 4.8.5, 4.9.4, 5.4.0, 6.4.0, 7.1.0, 8.0.1
  • GCC, C++14: 5.4.0, 5.5.0, 6.3.0, 6.4.0, 7.1.0, 7.3.0, 8.0.1, 8.1.0
  • GCC, C++17: 7.3.0, 8.0.1
  • Intel, C++14: 18.0
• OS X:

  • Apple Clang: 9.0.0, 9.1.0, 10.0.0
  • Apple Clang, C++11: 9.0.0, 9.1.0, 10.0.0
  • Apple Clang, C++14: 9.0.0, 9.1.0, 10.0.0
  • Apple Clang, C++17: 9.1.0, 10.0.0
  • Apple Clang, C++1z: 9.0.0
  • Apple Clang, C++2a: 10.0.0
• Windows:

  • GCC: 3.4.5, 4.1.2, 4.2.4, 4.3.3, 4.4.0, 4.5.4
  • GCC, C++0x: 4.6.4
  • GCC, C++11: 4.7.3, 4.8.1, 4.9.3
  • GCC, C++14: 5.1.0, 5.2.0, 5.3.0, 6.1.0, 6.2.0, 6.3.0, 6.4.0
  • GCC, C++17: 7.1.0, 7.2.0, 7.3.0
  • Visual C++: 7.1, 8.0, 9.0, 10.0, 11.0, 12.0, 14.0, 14.1
• FreeBSD:

  • Clang: 4.0.0
  • Clang, C++11: 4.0.0
  • Clang, C++14: 4.0.0
  • Clang, C++1z: 4.0.0

Acknowledgements

Marshall Clow, Michael Caisse and Glen Fernandes managed this release.