extern crate owning_ref;

use std::collections::HashMap;
use std::collections::hash_map::Entry;

use owning_ref::OwningRef;

struct Foo {
    v: OwningRef<String, str>,
    // Other data not important for the question
}

fn main() {
    let mut l = Vec::<Foo>::new();
    let mut hash = HashMap::<&str, usize>::new();

    for i in (0..10).chain((0..10).rev()) {
        let s = format!("aaa {}", i);
        let s = OwningRef::new(s);
        let foo = Foo { v: s };
        let sref = foo.v.as_ref();
        let idx = match hash.entry(sref) { //a
            Entry::Occupied(ent) => {
                *ent.get()
            }
            Entry::Vacant(ent) => {
                l.push(foo); //b
                ent.insert(l.len() - 1);
                l.len() - 1
            }
        };
        // do something with idx
    }
}