Rust barely even trying on the pluggable allocators (seems like it's never going to land, afaik "allocator-api" has been sitting proposed in nightly only since 2018) is one of the things that frustrates me (fulltime Rust eng) about the language and makes me feel like it's just a language that's been eaten by web services developers, applications level work, and/or tokio, and isn't "serious" as a systems PL really despite the verbiage.

Building a database, operating system, etc. absolutely requires fine tuned control over allocation. You can get around some of these things in Rust, but it will fight you. You'll effectively have to turn your back on the containers in std and build your own vectors, maybe even your own Box, etc.

Odin looks really appealing to me at one level, but I'd have a hard time switching to any language at this point that doesn't have a borrow checker story.

> My angle is systems programming, and there, it absolutely matter. If you are performance sensitive, then you try to avoid crossing the user-space -> kernel boundary more than you have to. Eg, ask for lots of memory, manage with arenas.

This gives the misleading impression that ordinary memory allocators are materially different from arena allocators. They aren't. Both types of allocators first ask for a big block of memory from the kernel, then dole that memory out in userspace. There's no need to cross the userspace/kernel boundary more often than you need to, especially when you consider that you can replace the standard platform allocator with whatever you want.

To wit, C doesn't emphasize arena allocation anywhere near as much as Zig et al do, and yet nobody alleges that C is somehow less suitable for systems programming than these languages. Have you considered why that is? Because, for the most part, arena allocation doesn't make a significant difference, and in the places where it actually does make a difference, you can trivially build an arena allocator on top of the standard allocator.