"Returns a value referencing data owned by the current function" inside match arms

Question

I want to retrieve a reference from a struct wrapped inside an enum. I should not clone or copy the data because i need only to read.

From what i understand the problem comes because i'm trying to return a reference of value contained in a temporary value (a and b) that are inside the match arms.

Link to the play ground to replicate the error: code

use std::cell::RefCell;
use std::rc::Rc;

enum Case<T: Custom> {
    A(Rc<RefCell<F<T>>>),
    B(Rc<RefCell<G<T>>>),
}

impl<T: Custom> Case<T>{
    pub fn get_u(&self) -> &T::U {
        match self {
            Case::A(a) => &a.borrow().u,
            Case::B(b) => &b.borrow().u,
        }
    }
}

trait Custom {
    type U;
}

struct F<T: Custom> {
    pub u: T::U ,
}


struct G<T: Custom> {
    pub u: T::U ,
}

struct H<T: Custom> {
    pub h: Case<T>,
}

impl<T: Custom> H<T>{
    pub fn foo(&self) {
        let u: &T::U = self.h.get_u();
        //read u and do stuff with it
    }
}

cargo build

error[E0515]: cannot return value referencing temporary value
  --> src/lib.rs:11:9
   |
11 | /         match self {
12 | |             Case::A(a) => &a.borrow().u,
13 | |             Case::B(b) => &b.borrow().u,
   | |                            ---------- temporary value created here
14 | |         }
   | |_________^ returns a value referencing data owned by the current function

error[E0515]: cannot return value referencing temporary value
  --> src/lib.rs:11:9
   |
11 | /         match self {
12 | |             Case::A(a) => &a.borrow().u,
   | |                            ---------- temporary value created here
13 | |             Case::B(b) => &b.borrow().u,
14 | |         }
   | |_________^ returns a value referencing data owned by the current function