I worked professionally with C, C++, Zig and Rust (in that order). My experience is that writing performant code is by far the easiest in C++, and by far the most difficult in C. Most of this, in practical experience, is due to ergonomics, in my opinion.

Templates in C++ benefit from being part of the core language, -- stick a `template` above your `class`, and you're in metaprogramming land. Stick a template specialization, and you've done a niche optimization. You didn't need a separate crate or a whole macro DSL. Variadic templates are also really really nice for monomorphizing N-ary generic functions. The duck typing of templates makes

This is precisely where I struggle with Rust the most -- monomorphization is limited within generics, so you end up going to the `proc_macro` hell, which involves a separate crate, a separate Cargo.toml, etc.

Zig seems like it would fit the bill -- and doing micro-optimizations within zig is surprisingly easy. The language's comptime facilities allow for really good niche optimizations -- however, the language also has some strange decisions. The allocator interface is notoriously a vtable, so a lot of the DOD optimizations that andrewrk has spoken numerously of (and to be clear -- I did learn a lot about DOD from his talks back when I was a wee engineer), raise one of my eyebrows.

C seems like it should be fast, but implementing any data structure, any generic algorithm in C is impossible. Either you're copy-pasting, or you're making macro DSLs. None of which is great.

---

To further talk about the C++ situation -- the monomorphic allocator interface was always awesome. Compared to Zig's vtables and Rust's nothing (up until a couple days ago), having a way to pass custom allocators with types was awesome. The new std::pmr::* interfaces and containers are also really exciting -- monomorphization, as beautiful as it is, does cost a lot -- refactoring it is not easy, compilation times are a mess. Sometimes the right tool is a vtable interface, and, C++ gives you those facilities.

And this is C++'s no1 problem when it comes to performance too -- it's a leviathan -- it'll give you the tools to write REALLY fast code, but it will also give you inheritance -- forget about your caches then.

When I was working at Tesla, there were some pretty gnarly vtable jumps in firmware (of all places), and I suspect part of that could've been alleviated if people knew more about CRTP.

So, here's where I land -- C++ really will give you the tools it can to let you write the fastest code possible. But it will also give you the tools to make your code really slow. Committee language means everyone in the committee needs to be happy.

Rust, on the other hand, is really designed to promote safe-but-very-fast practices -- had the firmware that I discussed used Rust, my guess is that we would've gravitated towards generics and monomorphization, rather than the heavy dynamic inheritance. C++, when it comes to performance, as it does to all other things, is a barreled shotgun. Rust's design almost always promotes the best available pattern and that's why I rarely reach out for C++.