Simple example of using an array of FnMut to execute inner code inside a trait object.

callback_executor.rs

pub trait Executor {
    fn run(&mut self, f: &mut dyn FnMut(i32) -> i32);
}

struct SimpleExecutor {
    v: i32,
}

impl Executor for SimpleExecutor {
    fn run(&mut self, f: &mut dyn FnMut(i32) -> i32) {
        self.v = f(self.v);
    }
}

fn use_executor<E: Executor, F: FnMut(i32) -> i32>(e: &mut E, mut f: F) {
    e.run(&mut f);
}

fn main() {
    let mut exec = SimpleExecutor { v: 2 };

    let mut ext = 0;

    {
        let mut fns: Vec<Box<dyn FnMut(i32) -> i32>> = vec![
            Box::new(|x| {
                ext += 1;
                x + 1
            }),
            Box::new(|x| x * 2),
            Box::new(|x| x * 3),
        ];

        for func in fns.iter_mut() {
            use_executor(&mut exec, func);
        }
    }

    println!("{}", exec.v);
    println!("{}", ext);
}