C++23BuildFixes

[ecbadeaux]

Intro:

This is a fix that ensures your project can successfully build with C++23 should you choose to upgrade. While exploring the project, I noticed that switching to a newer C++ version caused build failures. This pull request addresses those issues, allowing you to safely bump your CMAKE_CXX_STANDARD to 23 if desired.

Technical Changes:

Here is a screenshot of the build errors I was encountering.

You can easily reproduce them in the docker container with the following changes I have in my branch BuildFailuresC++23.

After inspecting the build errors, I was able to see that you were attempting to overload the stream insertion operators for the classes Tag, Id, and Measurement. In each of these classes, you were defining the implementation for the stream operator, which inherently would call the templated fmt::format specialization for each class. The issue is that the definition for each stream insertion would attempt to call the format specialization before it had been defined. In order to get around this error, you need to define the template before defining the stream insertion because of their dependencies.

I also removed the unneeded friend qualifier for the Id stream operator.

After making the changes above, I was able to get the project to build with C++23 🎉.

I've created a branch here that has an additional dummy unit test to ensure C++23 features are now working. This C++23 feature is only available in gcc-14, but, nevertheless, the project will now build with certain C++23 features if supported by the compiler version.

I did not bump the CMAKE_CXX_STANDARD, but if you would like me to, let me know 😄

[copperlight]

This is actually really helpful! I had been interested in bumping from C++17 to C++20 or C++23, but I kept running into build issues, which are related to how we were using fmt templates.

Internally, we still need to build on some old OSes - bionic and centos7. If we can get gcc-14 installed after-market on those platforms, then we can bump the CMAKE_CXX_STANDARD. Since we specify -static-libstdc++, we are protected from changing libstdc++ versions in the binaries when we run on these older OSes.

Taking a look this morning!

[ecbadeaux]

Glad I could help!

This pull request is safe to go ahead and merge if you want. We could circle back to upgrading the CXX version at your discretion.

I can look into making a script to get gcc14 working for those systems if you want. Just share the output for 'etc/os-release' on those systems