Iterating over a vector of mutable references to trait objects

Question

I have a struct that holds mutable references to trait objects:

trait Task {
    fn do_it(&mut self);
}

struct Worker<\'a> {
    task         


        

Answer 1

You need to have a mutable reference to each item. iter returns immutable references. And a immutable reference to a mutable variable is not itself mutable. Use iter_mut or for task in &mut self.tasks instead.

Then, the easiest thing to do is to inline work_one into work:

pub fn work(&mut self) {
    for task in self.tasks.iter_mut() {
        task.do_it()
    }
}

Unfortunately, splitting this into two functions is quite painful. You have to guarantee that calling self.work_one will not modify self.tasks. Rust doesn't track these things across function boundaries, so you need to split out all the other member variables and pass them separately to a function.

See also:

• cannot borrow `self.x` as immutable because `*self` is also borrowed as mutable
• Why are borrows of struct members allowed in &mut self, but not of self to immutable methods?