Difference between revisions of "User:Dydzio/cpp standard upgrade"

Revision as of 19:47, 22 June 2019

As of 22.06.2019 - linux debian will receive next stable version in few weeks and its GCC will upgrade from 6.3 to 8.3. Ubuntu 18.04 supports GCC 7.4, [AVS] currently uses GCC 7.3.

Scripting branch breaks VS 2015 compatibility by (bug/lack of C++ feature/whatever) in ERM parser. VS 2017 (MSVC 19.1x) has way better C++ support and there is almost no reason to still use 2015.

If we assume GCC 7.3 (GCC 7) as minimal supported GCC version then on GCC part we can use:

- full C++14 (also in GCC 6 if we do not want GCC 7 for some reason)

- almost full C++17, with exception of few features listed below, with optional examples of related standard library elements in braces:

• Polymorphic memory resources (<memory_resource>)
• C++17 should refer to C11 instead of C99
• Elementary string conversions (std::to_chars, std::from_chars, chars_format)
• Standardization of Parallelism TS
• File system library (std::filesystem)
• Template argument deduction for class templates - only partial support, probably conforms to v1 / draft paper?
• std::char_traits<char> and std::char_traits<wchar_t> in constant expressions.

There is no guarantee this is everything, travis CI should help. If somebody uses "not fully supported" feature on purpose he should let others know in PR description / slack etc.

Some sources:

• https://en.cppreference.com/w/cpp/compiler_support
• https://gcc.gnu.org/projects/cxx-status.html#cxx1z

If we decide to use Visual Studio 2017 as minimum supported VS version then we can use:

- full C++14

- vast majority of C++17 (microsoft claims "full comformance but with bugs" in VS 2017)

Apart from cppreference page... full conformance overview for VS 2015/2017/2019 is available on https://docs.microsoft.com/en-us/cpp/overview/visual-cpp-language-conformance?view=vs-2019

Especially watch out for following stuff in Visual Studio 2017:

• Preprocessor misbehavior, especially using variadic macros - last C++11 conformance bug, fixed in VS 2019
• Some bugs in advanced lambda usage, also fixed in VS 2019 - not directly C++17 related
• std::is_constant_evaluated() not working - C++17 related

Other not working stuff in VS2017 (C++17 related):

• LWG 2221 Formatted output operator for nullptr
• P0961R1 Relaxing the structured bindings customization point finding rules
• P0969R0 Allowing structured bindings to accessible members
• P0588R1 Simplifying implicit lambda capture
• P0962R2 Relaxing the range-for loop customization point finding rules
• P0929R2 Checking for abstract class types
• P1009R2 Array size deduction in new-expressions
• P1286R2 Contra CWG DR1778