Code shared from the Rust Playground

playground.rs

use std::cell::RefCell;
use std::collections::HashMap;

struct Bar<'a> {
    p: HashMap<String, RefCell<u8>>,
    _map: HashMap<u8, Vec<&'a RefCell<u8>>>,
}

impl<'a> Bar<'a> {
    fn new() -> Self {
        Bar {
            p: HashMap::new(),
            _map: HashMap::new(),
        }
    }
    
    fn foo(self: &mut Self) {
        match self.p.get("a") {
            Some(e) => {
                // push an element in the vec contained in _map at key "8"
                // here e is a ref on the refcell
                let v: &mut Vec<&'a RefCell<u8>> = self._map.entry(8u8).or_default();
                v.push(e);
                
                // from what I understand, e has the lifetime of p and it does not match with 'a
                // but since lifetime of p is equal to lifetime of self which is equal to 'a
                // I don't understand why it bugs here ...
            }
            None => {}
        };
    }
}

fn main() {
    println!("Hello, world!");
}