Here's how you can do global mutable state in Rust: #[macro_use] extern crate lazy_static; use std::sync::Mutex; lazy_static! { static ref ARRAY:

Here's how you can do global mutable state in Rust: #[macro_use] extern crate lazy_static; use std::sync::Mutex; lazy_static! { static ref ARRAY: Mutex<Vec<u8>> = Mutex::new(vec![]); } fn do_a_call() { ARRAY.lock().unwrap().push(1); } fn main() { do_a_call(); do_a_call(); do_a_call(); println!("called {}", ARRAY.lock().unwrap().len()); } I agree that this isn't the most ergonomic, but like most unergonomic things in Rust, there are reasons for it being so.