Lemon c++20 compatibility patch

[Alpar Juttner]

From Kevin Tew:

This feature was remove in c++20. ​https://en.cppreference.com/w/cpp/memory/allocator/destroy replace with ​https://en.cppreference.com/w/cpp/memory/allocator_traits/destroy

[Alpar Juttner]

Will that work with older C++ standards?

[David Torres Sanchez]

This doesn't work on C++20 as the construct method has also been removed. One can use the traits, in the same way as destroy, and it seems backwards compatible with older standards.

I get all sorts of other breaking changes from the maps_test on MSVC.

[David Torres Sanchez]

Mostly clang-format (sorry!), added AllocatorTraits::construct and destroy

[Alpar Juttner]

The attached 93c983122692.patch​ is a reworked version of ticket631.diff​. A basically removed the whitespace and reformatting changes. Now it can be seen what has actually changed.

One specific comment. I don't like the comment after the closing curly bracket like this

}; // end class StaticPath

In one hand, it is superfluous as most advanced editor can automatically show this information. On the other hand it is dangerous because it easily gets out of sync with the reality.

[Alpar Juttner]

Could anyone tell me if these changes are compatible with the older standards (with C++17, C++11 or even with C++98)?

[David Torres Sanchez]

Thanks Alpar!

From the C++ reference, it should be OK as far back as C++11 as it says in the docs for ​std::allocator_traits::construct. You can check it yourself in a clean build by changing the standard on lemon/CMakeLists.txt lines 76 and 81 (on your latest #658 patch).

[David Torres Sanchez]

I've come across a strange issue which I think stems from this. Basically gcc/g++-9 test fails because of test/lgf_reader_writer_test.cc on ubuntu-20.04 but not for example debian or archlinux.

To reproduce this on an ubuntu machine do:

CC="/usr/bin/gcc-9" CXX="/usr/bin/g++-9" cmake -S . -Bbuild
cmake --build build --target all
cd build && ctest --verbose

Alternatively, use the patch I'm about to submit with docker images, run (with docker and docker-compose installed)

cd docker
docker-compose up --build lemon-ubuntu

ubuntu can be replaced with debian, alpine or archlinux.

In either case, for ubuntu, you should see the error:

24: Test command: /home/lib/build/test/lgf_reader_writer_test
24: Test timeout computed to be: 10000000
24: terminate called after throwing an instance of 'lemon::FormatError'
24:   what():  lemon:FormatError: Item not found
24/44 Test #24: lgf_reader_writer_test ...........Child aborted***Exception:   0.30 sec

[David Torres Sanchez]

Add docker files with some linux distros

[David Torres Sanchez]

Alternatively, use the patch I'm about to submit with docker images, run (with docker and docker-compose installed)

​docker.patch <- here it is.