feat: quantity_kind and quantity_point_kind

[JohelEGP]

Resolves #173.
Partially addresses #172.
Resolves 3239186#r45824165.

[JohelEGP]

I still need to deal with MSVC and UNITS_DOWNCAST_MODE.

You'll notice that I chose to actually instantiate stuff rather than just checking their signature with type traits/concepts/require clauses. That's what led me to find the inconsistencies in (lack of) warnings.

Similarly, I test the validity of individual expressions in the tests' concepts. Remember when quantity didn't model std::equality_comparable due to the lack of a std::common_type specialization, and yet == was used everywhere? I'm basically testing that we don't accidentally provide a nonsensical ==, whereas testing with std::equality_comparable could fail for whatever reason. That's because it checks many things in addition to the expressions.

[mpusz]

Just as a reminder UNITS_DOWNCAST_MODE=OFF still does not work.

[JohelEGP]

By the way, I got this when using fmt's master branch. The quantity formatter uses a removed fmt::detail:: name.

../../../example/glide_computer.cpp:144:17:   required from ‘void {anonymous}::print(const R&) [with R = std::array<{anonymous}::glider, 4>]’
../../../example/glide_computer.cpp:380:16:   required from here
/home/johel/Documents/C++/Forks/mpusz/units/src/src/include/units/format.h:91:73: error: ‘make’ is not a member of ‘fmt::v7::detail::fill_t<char>’

[JohelEGP]

Actually, that was using my system-wide fmt, the latest stable release at the time.

[mpusz]

Should be fixed now with f9b15dd

[JohelEGP]

Can you confirm that this supports UNITS_DOWNCAST_MODE well?

[JohelEGP]

I agree with #100 (comment). I'll be removing those. I started using this PR, and instead of quantity_kind(my_kind{}, ...), I find myself using alias templates, like how example/glide_computer.cpp uses type aliases.

[JohelEGP]

I have taken a liking to doing something like unit_constants for quantity kinds. I call it variable_definition for now.

inline constexpr variable_definition<width> w{};
template <units::basic_fixed_string> auto operator""_v();
template <> auto operator""_v<"λ">() { return variable_definition<wavelength>{} };

f(w = 42 * m);
g("λ"_v = (42 * m / s) / (42 * Hz));

It is meant to mirror the lhs of math formulas. And to make quantity kind creation less verbose, similar to unit constants.

Would you be opposed to having something like this?

[mpusz]

WOW, this is HUGE!!! :-D

Thank you so much!!!

[mpusz]

Should be fixed now with f9b15dd

[mpusz]

Now we need some docs 😉

[JohelEGP]

What exactly? The PR did include some, mirroring quantity_point's.

[mpusz]

Sorry, my fault. The docs were there but they were not added to TOC.

[JohelEGP]

I thought I had done it:
https://github.com/mpusz/units/pull/204/files#diff-5b31041ef4b51a5ffbdf42e822a8b885f6e3ac8ed6b06b3958417f50a35a8a15R73

I see now that there's some repetition involved.

Perhaps using actions/upload-artifact to upload the generated documentation could help alleviate this in the future. That way, contributors who don't setup conan and everything else can still confirm that everything looks good.

[mpusz]

Agree, we could try to setup actions/upload-artifact for https://github.com/mpusz/units/actions?query=workflow%3ADocumentation when not run from the master branch. However, the artifact will be just *.zip archive. Do you think that contributors will be willing to download, extract, and verify them?

[JohelEGP]

The more documentation in the PR, the more likely that is.

[mpusz]

Isn't it easier to build and fix the docs locally? For example, what is the reason you are not doing so? Please note that some time ago I added UNITS_BUILD_DOCS CMake cache variable. With this, you can install Conan dependencies with build_docs=true and then disable the docs in CMake and enable only when needed.

[JohelEGP]

I think it may have been the struggle of using a new tool, namely Conan, in the past. I'll try it again, though.

[mpusz]

Thanks, just follow https://mpusz.github.io/units/usage.html#contributing-or-just-building-all-the-tests-examples-and-documentation. And please let me know in case of issues.