Reuse a `Vec<T>'s` allocation beyond the scope of its content

help
4

An ad-hoc implementation of the approach @kpreid mentioned to your example code looks like this

let mut empty_v: Vec<&str> = Vec::new();

loop {
    let mut v = empty_v;

    let data = String::from("Hello, world!");

    // Fill the vector with some data bound to the scope of the loop.
    v.push(data.as_str());

    // sanity check: address stays the same
    println!("{:p}", &v[..]);

    // Do things with the data.
    for s in &v { /* ... */ }

    // Clear the vector, ensuring there is no references left in the vector.
    v.clear();
    empty_v = v.into_iter().map(|_| unreachable!()).collect();
}

(adapted from @kpreid's solution above as well as the code in a previous post of mine here)

Note that (as explained in the other post and subsequent discussion) you can skip the into_iter+collect step on the take side due to variance.