Outside of single-initialization/lazy-initialization (which are provided via safe and trivial standard library APIs: https://doc.rust-lang.org/std/sync/struct.LazyLock.html ) almost no Rust code uses global mutable variables. It's exceedingly rare to see any sort of global mutable state, and it's one of the lovely things about reading Rust code in the wild when you've spent too much of your life staring at C code whose programmers seemed to have a phobia of function arguments.