Are you using macros with low-level code?

I'm curious about how Rust macros are being used for very low-level programming. I'm currently planning some changes to the macro system and this is a domain where I am not familiar. If you've been writing a kernel, device driver, or something similar and you've used Rust macros, please tell me about your experience! Did they do the job? Was there friction anywhere? Are there areas where C macros are traditionally used where Rust macros were more awkward?

Thanks in advance!

I am building kprintln! in the same way as println!, as is @phil-opp:

I am pretty bad at macros, but it was easy to write, and works well. The format machinery is so nice... not having to write out all that stuff is just amazing.

I'm writing a toy OS in Rust, and I've used a number of macros. I ended up using a bunch of macros to implement traits for some types, kernel-level println! like @steveklabnik's, and a couple other simple macros to avoid writing repetitive code. Just like in other Rust projects, I've had a pretty good experience using macros. It's nice that Rust's macros, unlike the C preprocessor, actually have some static checking to make sure they're reasonable.

Do proofs of concept like wom count? It uses a macro (wom!) to allow write-only access to struct fields when the base struct is write only. The macro uses an unsafe block, so it can't be used in no-unsafe crates even though it exposes a perfectly safe abstraction.

Do you mean macro_rules! only, or also compiler plugins? Apparently Zinc is heavily based on the latter:

I use macros quite extensively with inline assembly in my current project. This allows me to avoid code duplication when generating many similar asm! blocks.

Here is an example.

Thanks for the links and comments everyone! Very useful, especially links to projects which use macros. You're all too positive :slight_smile: Has anyone found things that don't work very well or which are frustrating to work with?

@steveklabnik - that link is broken. By "format machinery" do you mean the concepts or the format! implementation stuff in the compiler/libs?

@SimonSapin both

Sorry, I just broke that link today. Here's the updated one, which should last a long time: