Older version/branch supporting C++20?

[ddevienne]

Hi. Glaze looks really interesting. But I'm limited to C++20, so no-can-do C++23 for a while still.
Thus I'd like to know if there's a no-longer-supported version of glaze that used to work on C++20?
Perhaps with less features, but still useful and fast. So is there? TIA, --DD

[stephenberry]

Version 3.0.0 began the move to C++23. So, you can use v2.9.5, albeit the library has advanced significantly since then.

I will note that Glaze lightly uses C++23 and works with compilers like GCC 12 and Clang 17. I'm curious, is this limitation due to not being able to use newer compilers, or being told to avoid C++23?

In the transition from C++20 to C++23 Glaze only dropped GCC 11 and I think Clang 15.

[ddevienne]

Thanks for the reply. This is a corporate env, I have no say on the platforms/compilers. We're on GCC12 and VS2022 (17.8) in C++20 mode. And unlikely to advance to C++23 for a while longer I'm afraid. We're usually 3 years behind, and that's actually good, for a corporate env. Sometimes we're forced to use the OS's native compiler, and given our large clients keep quite old OSes around, that means very old compilers sometimes...

If by "lightly uses C++23" you mean meaningful parts of it would work in C++20, that sounds good. But I doubt it will be workable in practice. I'll look into 2.9.5, thanks for the link.

[stephenberry]

Thanks for your explanation, it's helpful to hear what is limiting.

I'd recommend 2.9.5 for your usage right now. The primary C++23 features that Glaze uses are:

• std::expected
• static constexpr variables within functions (C++20 does not allow constexpr variables to be static)

[ddevienne]

I guess I could use a polyfill like https://github.com/TartanLlama/expected for std::expected, but can't the constexpr keyword be simply dropped for in-function-static variables, trading compile-time for runtime initialization? I.e. the constexpr is just an optimization, and not fundamental, no? Just thinking aloud.

[stephenberry]

Glaze used its own expected type for a while, so the use of std::expected is actually more recent and only made because all compilers needed for that version of Glaze also had std::expected support.

It would be possible to move compile time calculations to runtime calculations using static const variables. However, these can be quite expensive in Glaze, because a lot of compile time work is done to find the optimal hashing algorithm for your fields.
Refactoring the code isn't really feasible, because Glaze uses template parameters for compile time known keys and much more. When the compiler knows lengths at compile time it can make functions like std::memcpy multiple times faster.
So, you would not just be paying for initialization costs, but even after initialization the runtime performance would be much slower.