Changes in gsl-lite
===================

version 0.42.0 2024-11-01

Additions:
- Define `gsl_MAYBE_UNUSED_MEMBER` for `[[maybe_unused]]` annotations on members
  (https://github.com/gsl-lite/gsl-lite/commit/34ba5141492a88912e2055e08cd1bdd6714431c5)
- Support `not_null<void*>` (#341, thanks to @BenFrantzDale)
- Support `not_null<>` for `unique_ptr<void, D>` and `shared_ptr<void>` (#349, thanks to @BenFrantzDale)

Changes:
- For modern (≥v1) defaults, `finally()`, `on_return()`, and `on_error()` are now implemented without virtual function calls (#342)
- Deprecate `finally()`, `on_return()`, and `on_error()` for pre-C++11 (#342)
- `narrow_failfast<>()` now uses `gsl_Assert()` rather than `gsl_Expects()` to express the contract check (#351)
- `std::hash<gsl_lite::byte>` now forwards to `std::hash<unsigned char>` (#343)
- Add Continuous Integration for GCC 13, Clang 17 to 19, and for NVCC 12.6; remove CI for GCC 10 on macOS and for
  Apple Clang 12.0.5 and earlier (#351)

Fixes:
- `std::terminate()` cannot be called from CUDA device code, but the call may go undetected due to a NVCC issue;
  for `!gsl_CONFIG( NARROW_THROWS_ON_TRUNCATION )`, `narrow<>()` now makes sure that the program is terminated by
  issuing a trap instruction if `std::terminate()` is not available (#351, thanks to @pauleonix for helping track this down)
- `narrow<>()` no longer responds to `gsl_CONFIG_CONTRACT_VIOLATION_THROWS` because it does not do contract checking;
  therefore, it now plainly fails to compile if `gsl_CONFIG_NARROW_THROWS_ON_TRUNCATION` is set to 1 even though
  exceptions are unavailable (e.g. in device code) (#351)
- Fix issues in test suite (#338, thanks to @musicinmybrain)

version 0.41.0 2023-04-12

Additions:
- Add tentative C++23 detection macro `gsl_CPP23_OR_GREATER`, `CONSTEXPR_23` language feature, and `gsl_constexpr23`
  keyword macro (#329)
- Add `gsl_CONFIG_VALIDATES_UNENFORCED_CONTRACT_EXPRESSIONS` config switch for suppressing the compile-time syntax
  validation of contract check expressions (#330)

Changes:
- Deprecate `string_span` and `zstring_span` and prepare for removal (#335)
- Continuous Integration now also tests GCC 12, Clang 14 thru 16, and NVCC 11.8 and 12.1
- Remove Continuous Integration for GCC 6 and earlier, Clang 5 and earlier, Apple Clang 11.0.0 and earlier, and
  CUDA 10.2 and earlier (#333, #334)

Fixes:
- Use NVCC's `__builtin_assume()` for `gsl_ASSUME_()` in device code (#324, thanks to @codecircuit)
- Fix `not_null_ic<>` copy construction (#326, thanks to @runer112)
- Respect libc++ configuration option to disable `wchar_t` (#331, thanks to @burnpanck)
- Suppress "-Wweak-vtables" warning for Clang (#332, thanks to @mrahn)
- Suppress "-Wuseless-cast" warning for GCC (#332, thanks to @wirew0rm)

version 0.40.0 2021-11-05

Additions:
- Add debug-mode contract checking macros `gsl_ExpectsDebug()`, `gsl_EnsuresDebug()`, `gsl_AssertDebug()` which are sensitive
  to the `NDEBUG` macro, and thus similar to `assert()` (#316)
- Add dedicated contract check configuration macros for device code: `gsl_CONFIG_DEVICE_CONTRACT_CHECKING_AUDIT`/`ON`/`OFF`,
  `gsl_CONFIG_DEVICE_CONTRACT_VIOLATION_ASSERTS`/`TRAPS`/`CALLS_HANDLER`, and
  `gsl_CONFIG_DEVICE_UNENFORCED_CONTRACTS_ASSUME`/`ELIDE` (#317)
- Add `gsl::is_valid()` for explicitly detecting the moved-from state of a `gsl::not_null<>` object (#318)
- Add device code detection macro `gsl_DEVICE_CODE` (evaluates to 1 when compiling CUDA device code, 0 when compiling host code)

Changes:
- Continuous Integration now also tests Clang 13 and updates CUDA version to 11.5
- Improve documentation for contract checking macros and configuration macros

Fixes:
- Check for `gsl::` target rather than nonexistent `gsl-lite::` target in Config.cmake (#315, thanks to @Ram-Z)

version 0.39.0 2021-09-30

Additions:
- Add `gsl::make_unique<T>()` and `gsl::make_shared<T>()` which resemble the eponymous functions from `std` but return
  `gsl::not_null<std::unique_ptr<T>>` and `gsl::not_null<std::shared_ptr<T>>` (#312)
- Add basic support for NVHPC compiler (#308, thanks to @olupton)

Changes:
- Continuous Integration now also tests GCC 11, Clang 12, and AppleClang 12.0.5 and 13, and updates CUDA version to 11.4 (#314)
- Remove C++98 polyfills `std98::equal()`, `std98::lexicographical_compare()` from public interface (#313)

Fixes:
- `gsl::not_null<std::shared_ptr<T>>` now correctly converts to `std::weak_ptr<T>` (#311, thanks to @stohrendorf)

version 0.38.1 2021-04-22

Additions:
- Add feature detection macro `gsl_HAVE( C99_PREPROCESSOR )`
- Add `gsl_CONSTRAINT()` which can be used to impose concept requirements on template type parameters in a backward-compatible manner:
  `template< gsl_CONSTRAINT(Concept) T >` expands to `template< Concept T >` for C++20 and to `template< typename T >` otherwise
- Add C++20 polyfill `std20::endian()` (#305)
- Restore Continuous Integration testing for NVCC 10.2
- Add basic CUDA runtime tests to test suite (#307)

Changes:
- Continuous Integration now also tests "RelWithDebInfo" configuration for select compilers and platforms

Fixes:
- Fix regression in precondition/postcondition/assertion checks for CUDA (cf. #302, thanks to @Spielix)
- Add workaround for GCC bug to test suite (cf. #303, thanks to @sanjayankur31)
- Fix endianness issues in test suite (cf. #304, thanks to @sanjayankur31)
- Improve `constexpr` support for `span<>`; add `constexpr` tests (#306)

version 0.38.0 2021-03-31

Additions:
- Add macros `gsl_Assert()`, `gsl_AssertAudit()` to express checks which are neither pre- nor postconditions (#294)
- Add fail-fast operation `gsl_FailFast()` which is guaranteed to terminate normal execution in some way
  (exception, `std::terminate()`, or trap instruction) (#294)
- Add configuration option `gsl_CONFIG_CONTRACT_VIOLATION_TRAPS` which makes `gsl_Expects()`/`gsl_Ensures()`/`gsl_Assert()` (and
  the `Audit` variants if audit mode is enabled) and `gsl_FailFast()` execute a trap instruction in case of a contract violation
- Add configuration option `gsl_CONFIG_CONTRACT_VIOLATION_ASSERTS` which implements `gsl_Expects()`/`gsl_Ensures()`/`gsl_Assert()`
  (and the `Audit` variants if audit mode is enabled) in terms of the `assert()` macro from the standard library. This has the
  benefits that both legacy assertions and contract checks can be globally suppressed with a single macro (`NDEBUG`), and that
  `assert()` prints an informative error message which contains the contract check expression.
- Add `as_nullable()` function (#251, thanks to @petamas)
- Add compiler detection macro for NVCC (#294)
- Add compiler detection macro and tentative support (no CI) for ARMCC (#293; thanks to @woodsking2)
- Add conditional `std::hash<>` specialization for `not_null<>` (#297; thanks to @mbs-c)
- Track language and library versions separately; new macros `gsl_STDLIB_CPPxx_OR_GREATER` indicate availability of the standard library
- Add feature detection macros `gsl_HAVE( HASH )`, `gsl_HAVE( MOVE_FORWARD )`, `gsl_HAVE( OVERRIDE_FINAL )`
- Add `size_type` to `span<>` and `basic_string_span<>`
- Add Continuous Integration testing for NVCC 11.0-11.2 (CUDA14, CUDA17), Clang 10-11, GCC 10, Apple Clang 12.0.0
- Add Continuous Integration testing for Clang with libstdc++
- Add Valgrind "memcheck" run to Continuous Integration
- Add testing for more configuration scenarios, e.g. building with exceptions disabled and using different ways of precondition
  violation handling

Changes:
- Remove dependency on standard library headers <algorithm> and <iterator> (#290, #295; thanks to @mpusz)
- Use of `gsl_HAVE()`, `gsl_CONFIG()`, `gsl_FEATURE()` with unknown arguments now causes compilation errors (#272)
- `narrow<>()` now issues a `static_assert()` that refers to `narrow_failfast<>()` if exceptions are unavailable (#269)
- With version-1 defaults, `not_null<>` now has a specialization for raw pointers which avoids unnecessary contract checks (#300)
- The contract expression is now part of the exception message in `gsl_CONFIG_CONTRACT_VIOLATION_THROWS` mode
- `narrowing_error` now produces a less unhelpful exception message ("narrowing_error")
- `gsl_noexcept` now falls back to `throw()` if `noexcept` is unavailable
- Most symbols are now accessible through both `namespace gsl` and `namespace gsl_lite` to ease migration
- `not_null_ic<>` is now also visible in `namespace gsl_lite` (#280; thanks to @woodsking2)
- `nullptr_t` comparison operators for `not_null<>` are now explicitly deleted
- More uses of `gsl_NODISCARD` throughout the library
- For NVCC ≥11.3, make use of new `__builtin_unreachable()` intrinsic in `gsl_CONFIG_UNENFORCED_CONTRACTS_ASSUME` mode

Fixes:
- Many bugfixes (#249, #250, #255, #256, #262, #263, #268, #270, #271, #286, #287, #292; thanks to @fodinabor, @KazDragon,
  @martinmoene, @Maximus5, @Pesa, @petamas, @travnick)

version 0.37.0 2020-05-13

Additions:
- Add configuration option `gsl_CONFIG_NARROW_THROWS_ON_TRUNCATION`
- Add configuration option `gsl_CONFIG_ALLOWS_SPAN_COMPARISON`
- Add `narrow_failfast<>()`, a fast-fail variant of `narrow<>()` (#52)
- Add `front()` and `back()` to `span<>` and `basic_string_span<>` (#241, thanks to @ned14)

Changes:
- Rename `as_writeable_bytes()` -> `as_writable_bytes()` to follow C++20 in spelling; the old name is still provided for compatibility
- Rename `gsl_DEPRECATED()` -> `gsl_DEPRECATED_MSG()`, add `gsl_DEPRECATED`
- Add more `gsl_DEPRECATED()` annotations
- Deprecate `span<>::at()`, `basic_string_span<>::at()`, and call indexing
- Minor documentation improvements
- Unify internal SFINAE macros to `gsl_ENABLE_IF_()` (#238; thanks to @martinmoene)
- Add more comprehensive tests for `narrow<>()` and `narrow_failfast<>()`

Fixes:
- Fix spurious static assertion for pre-/postcondition check arguments explicitly convertible to bool if `gsl_CONFIG_CONTRACT_CHECKING_OFF` is defined
- Fix hard failure in `span<>` constrained constructor (#242, thanks to @orangeturtle739)
- Make `gsl::detail::is_compatible_container<>` a proper type trait


version 0.36.0 2020-01-24

The repository now moved to a dedicated GitHub organization: https://github.com/gsl-lite/gsl-lite

gsl-lite is now mostly maintained by @mbeutel (#175).

Additions:
- Describe versioning semantics in Readme
- Add audit-level contract checks `gsl_ExpectsAudit()` and `gsl_EnsuresAudit()` (#172)
- Add `basic_zstring_span<>` and `zstring_span` (#136, #154, thanks to @chan-lee)
- Add support for user-defined contract violation handler `fail_fast_assert_handler()`
- Add macros `gsl_NORETURN`, `gsl_NODISCARD`, `gsl_DEPRECATED()`, `gsl_constexpr17`, `gsl_constexpr20`
- Add C++11 polyfills in `gsl::std11`: `remove_reference<>`
- Add C++17 polyfills in `gsl::std17`: `conjunction<>`, `disjunction<>`, `negation<>`, `void_t<>`
- Add C++20 polyfills in `gsl::std20`: `identity`, `type_identity<>`, `ssize()` (#144, #180), `remove_cvref<>`
- Add configuration macro `gsl_CONFIG_TRANSPARENT_NOT_NULL` (#185)
- Add configuration macro `gsl_CONFIG_INDEX_TYPE` which controls the type of `gsl::index` independently of `gsl::span<>::index_type` (#169)
- Add language feature macro `gsl_HAVE_EXCEPTIONS`
- Add macros `gsl_DEFINE_ENUM_BITMASK_OPERATORS()` and `gsl_DEFINE_ENUM_RELATIONAL_OPERATORS()`
- Add header <gsl-lite/gsl-lite.hpp> and namespace `gsl_lite` to pave the way for future coexistence with M-GSL (#221, #222)
- Add Continuous Integration for more versions of GCC (4.7 through 9), Clang (3.5 through 9), AppleClang (7.3 through 11), and MSVC (2010 through 2019)
- Run tests with AddressSanitizer and UndefinedBehaviorSanitizer in CI (GCC 9, Clang 9)
- Add Continuous Integration for NVCC 10.2 (with GCC 7, 8 on Linux, MSVC 2019 on Windows) to test CUDA support

Changes:
- `not_null<>` now properly supports smart pointers (#184, #197, huge thanks to @petamas)
- Restructure contract checking configuration macros such that checking policy (off, on, audit), violation handling (throws, terminates, calls handler) and unenforced contract handling (assume, elide) can be configured independently (cf. https://github.com/martinmoene/gsl-lite/#contract-violation-response-macros)
- `gsl_noexcept` no longer depends on contract violation settings (cf. https://github.com/martinmoene/gsl-lite/commit/0c296a9c986ac070997610fc7cf86e9c517558bf)
- `gsl_FEATURE_IMPLICIT_MACRO` now defaults to 0 (#156, thanks to @tadeu)
- AppleClang is now considered a separate compiler (use `gsl_COMPILER_APPLECLANG_VERSION` for checking)
- CMake installs arch-independent by default
- CMake doesn't install M-GSL compatibility headers by default
- gsl-lite now compiles warning-free with MSVC at warning level 4
- Many small improvements (thanks to @AraHaan, @codecircuit, @elnull, @ilyalesokhin-starkware, @ngrodzitski, @petamas, @stohrendorf, @theodelrieu)


version 0.34.0 2019-03-21

Additions:
- Add macro gsl_REQUIRES_T() (nonstd lite issue 18)

Changes
- Change the CMake package folder name to gsl-lite (it was gsl)
- Add a usage description for the Conda package manager to the Readme.
- Update lest test framework to v1.35.1.


version 0.33.0 2019-03-08

Additions:
- Add script/create-cov-rpt.py to create OpenCppCoverage report (nonstd-lite project issue 29)
- Add script/create-vcpkg.py (nonstd-lite-project issue 28)
- Add script/upload-conan.py (nonstd-lite-project issue 26)
- Add conanfile.py, edit it from script/update-version.py (nonstd-lite-project issue 26)
- Add CMake installation and config-file packaging; Let tests and example use gsl-lite interface library
- Add "LANGUAGES CXX" to CMake project
- Add GNUC -Wsign-conversion warning to CMake configuration
- Add AppleClang to CMake configuration
- Add OSX to Travis configuration
- Add TOC entry for Standard selection macro (#128, thanks to @egarrulo)
- Add span::ssize(), ssize(span), size(span) (#144)
- Add test/tc-cl.bat

Changes:
- Rename "Guideline support library" to "Guidelines -" (#134)
- Align Appveyor configuration (plan 9, nonstd-lite-project issue 14)
- Align CMakefiles.txt (plan 8, nonstd-lite-project issue 13)
- Align test scripts (nonstd-lite-project issue 12)
- Align badges in readme (nonstd-lite-project issue 3)
- Obviate need for -DNOMINMAX with MSVC (nonstd-lite issue 16)
- Prevent and suppress warnings from clang
- Let ctest produce output on failure
- Update lest test framework to v1.35.0.

Fixes:
- Fix CMake install command (expected-lite issue 25, thanks to @rmorozov)
- Fix clashing CMake cached variable, use 'gsl' for namespace and package folder (thanks to @rmorozov)
- Fix template argument in not_null<> comparison operators (#143, thanks @stohrendorf)
- Fix macro gsl_IN_STD (#142, thanks to @Flamefire)
- Fix possible int overflow in nonstd::span::subspan() range (issue #138, thanks to @fefe17)
- Fix link to P0122 (#130, thanks to @alexeyr)
- Fix for misleading __cplusplus of GCC 4.7.0 and earlier (#127, thanks to @egarrulo)
- Fix final_action_return() and final_action_error() during stack unwinding (#126, thanks to @patstew)
- Fix unused parameter if Expects elided via new macro gsl_EXPECTS_UNUSED_PARAM (#123, #124, thanks to @kugelrund)

version 0.32.0 2018-05-12

- Review not_null (issue #122).
- Add not_null_ic with implicit constructor, allowing copy-initialization.
- Enable making not_null constructor explicit via gsl_CONFIG_NOT_NULL_EXPLICIT_CTOR, default 0 (breaking, issue #46).
- Enable not_null get() return by const & via gsl_CONFIG_NOT_NULL_GET_BY_CONST_REF (via M-GSL PR 651 @xaxxon, PR 675 @ericLemanissier).
- Change constraint on not_null construction from is_convertible to is_constructible (via M-GSL PR 650, @xaxxon).
- Change to take not_null constructor argument by const & when rvalue references are not available.
- Add not_null non-is-default rvalue reference copy-constructor, copy-assignment.
- Remove not_null converting assignment operator.
- Rename to gsl_HAVE_EXPLICIT.
- Adapt several compile-time tests for not_null with explicit constructor.
- Fix GNUC C++98 compilation by making RefCounted conversion function const in not_null.t.cpp.

version 0.31.0 2018-05-10

- Change span towards proposal p0122r7 (issue #118).
- Add gsl_lite_MAJOR, gsl_lite_MINOR, gsl_lite_PATCH, script/update-version.py.
- Add configuration selector gsl_CONFIG_DEPRECATE_TO_LEVEL.
- Add feature selector gsl_FEATURE_WITH_CONTAINER_TO_STD.
- Add feature selector gsl_FEATURE_MAKE_SPAN_TO_STD.
- Add feature selector gsl_FEATURE_BYTE_SPAN_TO_STD.
- Add macros gsl_FEATURE(), gsl_CONFIG(), gsl_HAVE().
- Add macro gsl_ADDRESSOF(x).
- Add span::value_type.
- Add details::can_construct_span_from<>.
- Add convertible constraint to span C-array constructor.
- Add class template argument deduction guides for span.
- Add make_span( with_container_t, ...) creator functions.
- Add byte_span() creator functions.
- Use C++11 constexpr where possible.
- Parenthesize macro arguments.
- Omit macros min(), max() via -DNOMINMAX.
- Update t-all.bat for various configuration and feature selections.

version 0.30.0 2018-05-06

- Add support for DJGPP cross compiler is introduced (PR #107, thanks to Tom� Zeman, @zemasoft).
- Add Readme.md to example/cmake-pkg.
- Update lest test framework to v1.33.1.
- Allow strict aliasing with Clang and GNUC for gsl::byte (issue #114).
- Enable differentiating between MSVC 14.0 (VS 2015) and 14.1 (VS 2017), also report clang version.
- Remove the space after ':' in FILE: LINE in reported locations (issue #112).
- Avoid MSVC level 4 warning C4127: conditional expression is constant (issue #115, thanks to @kpeace)
- Add a constructor to allow rvalue to const lvalue conversion (issue #113, PR #117, thanks to @theodelrieu )
- Enable owner alias template for VC12 (Issue #111, thanks to @sg-james)
- Fix omission of #include <algorithm>
- Fix clang compilation by specifying C++ standard
- Fix gsl-lite version in section "As CMake package"
- Fix type in a test of span has been correced (PR #105, thanks to Tom� Zeman, @zemasoft)

version 0.29.0 2018-03-03

- Added CMake package, thanks to @FlorianWolters (PR #100, #103).
- Added CMake option GSL_LITE_OPT_BUILD_TESTS to ./CMakeLists.txt (default off).
- Added CMake option GSL_LITE_OPT_BUILD_EXAMPLESto ./CMakeLists.txt (default off).
- Added scipt/install-gsl-pkg.py
- Added script use-gsl-pkg.py as part of an example that uses the package.
- Added script/update-version.py to updated gsl-lite's version number in relevant files.
- Added type `gsl::index` for container indices, subscripts and sizes.
- Fixed padding of the output stream operator of class `string_span` to pad to the right side.
- Deprecated span::length() and span::length_bytes() (issue #99).
- Deprecated constructors span(shared_ptr<element_type> const & ptr) and span(unique_ptr<element_type> const & ptr)` (issue #98).
- Added documentation section 'Deprecation'.
- Expanded documentation section 'Installation and use'.
- Updated documentation section 'Reported to work with'.

version 0.28.0 2018-01-01

- Expand Travis and Appveyor CI compiler matrices and use CMake configuration.
- Fix to use CMAKE_CXX_COMPILER_VERSION in CMake configuration.
- Add targets for various -std flags for MSVC to CMake configuration.
- Add Core Guidelines checking, limited to GSL Lite.
- Add test to compare empty to non-empty string span.
- Suppress test to compare empty string spans.
- Update Wandbox link for release 0.28.0.
- Update Wandbox link for release 0.27.0.

version 0.27.0 2017-12-30

- Change extension of GSL Lite header file to .hpp with backwards compatibility via headers gsl.h and gsl/gsl-lite.h. See issue #94 (thanks to @AraHaan).
- Suppress several warnings from Microsoft's CppCoreCheck. See pull request #95 (thanks to @AraHaan).

version 0.26.0 2017-12-09

- Rename final_act to final_action per issue #89.
- Make clang-tidy cppcoreguidelines checks pass per PR #91 (thanks to @poconbhui).
- Fix nullptr to gsl_nullptr in not_nul::get() per PR #90 (thanks to @poconbhui).
- Fix -Wshadow warning per PR #84 (thanks to @MikeLankamp).
- Add conan installation instructions and badge (thanks to @agauniyal).
- Add CMake install target per issue #85.

version 0.25.0 2017-10-22

- Restrict owner<T> to pointers if possible, per issue #80.
- Introduce gsl_is_delete, per issue #81.
- Add deleted operators for not_null<>, per issue #82.
- Add more comparison operators for not_null<>, per issue #83.
- Use = default for not_null copy assignment/construction if available.
- Take parameter in not_null assignment by value as in ctor.

version 0.24.0 2017-07-10

- Add try it online badge.
- Implement to_byte(), to_integer() for C++17 per issue #75 (thanks to David Mugnai, @cinghiale).

version 0.23.0 2017-06-29

- Enable use of option -Wundef per issue #74.
- Update lest to version 1.30.1.
- Check macro via #ifdef if possibly undefined (support -Wundef).
- Fix check for make_unique().
- Fix CMake compiler selection.
- Make struct definition nonlocal for C++98, C++03.
- Add not_null<> tests for member access and dereferencing.
- Add dereference operator to not_null<> per issue #73.
- Add compiler version information.
- Add constexpr to not_null<>.
- Report gsl_CPP11_OR_GREATER etc.

version 0.22.0 2017-04-27

- Add operator<< for string_span (thanks to Magnus Bergsten, @Sillamacka).
- Fix conversion and sign-conversion warnings (thanks to Magnus Bergsten, @Sillamacka).
- Fix memory leak, which prevents tests to pass with address sanitizing (thanks to @Vladimir Rapatskiy).
- Fix order of add_compile_options() and its targets in CMakeLists.txt.
- Replace fail_fast's base with std::logic_error as per issue #69.
- Update lest_cpp03.hpp to version 1.29.1 (Fix above conversion and sign-conversion warnings).

version 0.21.0 2016-11-28

- Add as_bytes() for basic_string_span<> (thanks to Magnus Bergsten, @Sillamacka).
- Fix: remove call to hash<std::size_t>(), undefined with Xcode on Mac OS X (issue #63, thanks to Dave Tallman).
- Fix: remove static from enum in integral_constant (thanks to Dave Tallman).
- Change t[g]-all.bat to test variations of C++ std/span index type/contract violation response.

version 0.20.0 2016-11-18

- Remove used_length(), same as length()
- Rename bytes(), used_bytes() to size_bytes(), length_bytes()
- Make final_act<T> and final_act_return<T> useable with VC11/VS2012 (PR #61, thanks to @lm1458777)
- Fix fail_fast_assert() for gcc < 6 for no-throw/std::terminate() case (comment, thanks to @xsacha)
- Fix =default with gsl_noexcept for gcc < 6 for basic_string_span (PR #58, thanks to @xsacha)

version 0.19.0 2016-11-17

- Rename as_span() creator functions to make_span() (issue #49).
- Add make_span() for gsl::shared_ptr, gsl::unique_ptr.
- Add section Algorithms to feature table.
- Remove maybe_null from feature table (M-GSL PR 123, 124, 126).

version 0.18.0 2016-11-11

- Remove span::size_type, deprecated since 0.12.0.
- Add gsl_CONFIG_SPAN_INDEX_TYPE configuration macro; default size_t.
- Add span constructor for std::array<> const &.
- Add span constructor for std::unique_ptr, std::shared_ptr.
- Make span's unconstrained constructor disabled at default.
  This enables construction from unique_ptr and shared_ptr.
- Prevent conversion warning [-Wconversion]
- Prevent old-style casts warning [-Wold-style-cast]
- Replace arr with &arr[0], not automatic decay (several).
- Update lest_cpp03.hpp to version 1.27.2
- Fix noexcept with default ctors for GNUC < 4.9.0 (adapted PR #58, thanks to Dmitry Banschikov, @ubique).

version 0.17.2 2016-11-10

- Use &arr[0], not automatic decay
- Workaround GNUC 5 throw constexpr bug
- Workaround for GNUC 5.2.0 failing two tests
- Use order: gsl_api inline gsl_constexpr type f() gsl_noexcept

version 0.17.1 2016-11-09

- Fixes thanks to Magnus Bergsten, @Sillamacka:
- Marked several functions as constexpr.
- Fix: make gsl::fail_fast_assert() constexpr allowing Expects() from constexpr functions.
- Fix: prevent pointer decay to let remove_z() invoke wrong overload.
- Fix: remove span used in string_length(), it has two bound problems.

version 0.17.0 2016-11-09

- Add free-standing as_bytes() and as_writable_bytes() as in M-GSL (PR #55, thanks to Dmitry Banschikov, @ubique).
- Member methods as_bytes() and as_writable_bytes() have been deprecated.

version 0.16.1 2016-11-09

- Fix macro used with string_span comparison.

version 0.16.0 2016-11-09

- Allow comparison with types that are convertible to string_span (issue #53, thanks to Magnus Bergsten, @Sillamacka).

version 0.15.0 2016-11-09

- Add basic_string_span (issue #53, thanks to Magnus Bergsten, @Sillamacka).

version 0.14.0 2016-11-03

- narrow() now uses std::terminate(), unless gsl_CONFIG_CONTRACT_VIOLATION_THROWS (issue #50, thanks to @Sp3EdeR)
- narrow_cast<>() now forwards its argument if possible (issue #44).

version 0.13.0 2016-10-09

- Add on_return() and on_error() as experimental feature (gsl_FEATURE_EXPERIMENTAL_RETURN_GUARD).

version 0.12.0 2016-10-08

- Fix test compilation with GCC 4.8.4.
- Remove span::value_type deprecated since version 0.9.0 (use element_type).
- Deprecate span::size_type (issue #42).
- Make span's stream output for tests more container-like.
- Make operations on byte C++11 constexpr except for op=() variants.
- Rename �Guidelines support library" to "Guideline -" (issue #39).
- Add tests for C++11 constexpr-ness.
- Add copy algorithm for span (issue #36).
- Add GSL version by Vicente J. Botet Escriba to Readme.

version 0.11.0 2016-09-04

- Add missing byte comparisons (non-enum class case).
- Add missing gsl_noexcept to byte equality operator.

version 0.10.1 2016-09-02

- Use struct with unsigned char for byte with pre-C++17 (issue #34).

version 0.10.0 2016-08-31

- Remove operator bool() per issue #33.
- Remove deprecated gsl_CONFIG_THROWS_FOR_TESTING.
- Remove parentheses and allow lest to decompose span comparison expressions.
- Allow comparison of spans with a different element type or const-volatile-ness.
- Add gsl_CONFIG_ALLOWS_NONSTRICT_SPAN_COMPARISON for span comparison configuration.

version 0.9.1 2016-08-25

- Move conditional inclusion of cstdint out of namespace gsl.

version 0.9.0 2016-08-23

- Provide gsl/gsl header for compatibility with M-GSL.
- Add index_type to span while keeping size_type.
- Add gsl_noexcept to iterator creators begin() etc.
- Add at(std::initializer_list<T>, index).
- Add at(span<T>, index).
- Add call operator to span for element access as per p0122r3.
- Add test: empty spans compare equal as per p0122r3.
- Use span's size_type.
- Move at() to section utilities.
- Move comparison functions outside span.
- Deprecate span::value_type, use span::element_type per M-GSL, p0122r3.
- Remove non-const index operator, at().

version 0.8.0 2016-08-20

- Add operations for byte type.

version 0.7.5 2016-08-08

- Fix to create empty subspan, enabling slicing off data until span is empty (PR #26, thanks to Janusz Chorko).

version 0.7.4 2016-07-09

- Revert "Remove boundary check from operator[]()" of v0.7.3.

version 0.7.3 2016-07-08

- Removed boundary check from operator[]()
- Changed indexing to return non-const reference and make it STL compliant (issue #23, thanks to @marton78)
- Made converting constructors public (issue #22, thanks to @marton78).

version 0.7.2 2016-07-06

- Fixed as_span() for const arguments (thanks to Dave Tallman).

version 0.7.1 2016-07-01

- Fixed with_container_t to be literal type (thanks to Dave Tallman).

version 0.7.0 2016-06-30

- Added tagged construction from a container to span.
- Replaced gsl_CONFIG_ALLOWS_SPAN_CONTAINER_CTOR with gsl_CONFIG_ALLOWS_UNCONSTRAINED_SPAN_CONTAINER_CTOR

version 0.6.1 2016-06-29

- Fixed library for the removal of _HAS_CPP0X in VS2015 Update 3 (Issue #21, thanks to @exjam)
- Added tests tagged [.stdlangauge], [.stdlibrary] to inspect various gsl_HAVE_... macros.
- Added tag [.stdc++] to test to inspect __cplusplus.
- Updated lest test framework to version 1.27.0.

version 0.6.0 2016-06-25

- Renamed Final_act to final_act to follow standard library conventions.
- Fixed final_act to also work without copy-elision optimization, issue #19 (thanks to Marco Arena).

version 0.5.0 2016-06-24

- Added compatibility with MS GSL symbolic names for contract violation response control.
- Added contract violation response control as suggested in N4415, Simple Contracts for C++.

version 0.4.1 2016-06-23

- Added gsl_CONFIG_ALLOWS_SPAN_CONTAINER_CTOR for pre-C++11 (default: 1).
- Avoided std::distance() to support CUDA.
- Avoided shadowing according to the too-strict option -Wshadow of gcc before 4.8 (thanks to Dave Tallman).
- Removed comparisons of unsigned with zero.
- Fixed ensure_z() without length (thanks to Dave Tallman).

version 0.4.0 2016-05-28

- Added support for CUDA compilation.

version 0.3.2 2016-05-27

- Fixed compilation error in narrow() for VC11 (VS2012).

version 0.3.1 2016-05-25

- Added test for construction of a span from another span of a compatible type.
- Changed view to span in specification.

version 0.3.0 2016-05-24

- Added first(), last() and subspan().
- Improved example 02-span.cpp (thanks to Dave Tallman).

version 0.2.2 2016-05-23

- Fixed missing return in not_null copy-assignment (thanks to PVS-Studio).

version 0.2.1 2016-05-23

- Added several tests.
- Added definition of gsl_HAVE_DEFAULT_FUNCTION_TEMPLATE_ARG.
- Prevented using default function template argument in span for pre-VS2013 (VC12).
- Fixed compile error with clang targeting MSVC, PR #17 (Thanks to @ned14).
- Fixed data access of empty container, PR #16 (Thanks to @realzhtw).

version 0.2.0 2016-02-02

- Removed constructor span( U (&arr)[N], size_type size ), not part of M-GSL and in favour of:
- Changed constructor to span( pointer data, size_type size ), removing & from pointer & data (Thanks to @realzhtw).
- Added construction from an l-value for C++11 onwards.

version 0.1.0 2016-02-02

- Added move-construction and move-assignment to span<>.

version 0.0 2015-09-25

- Initial release.