Rust Lifetime problems

Sharing value with lifetime

#[derive(Debug)]
struct Value(i32);

#[derive(Debug)]
struct Shared<'a> { val: &'a Value }

#[derive(Debug)]
struct A<'a> {
    shared: &'a mut Shared<'a>,
}

struct B<'a> {
    shared: &'a mut Shared<'a>,
}

impl<'a> A<'a> {
    fn new(shared: &'a mut Shared<'a>) -> Self {
        A {
            shared: shared,
        }
    }
}

impl<'a> B<'a> {
    fn new(shared: &'a mut Shared) -> Self {
        B {
            shared: shared,
        }
    }

    fn make_a(&mut self)  -> A {
        let a = A::new(self.shared);
        a
    }
}

fn main() {
    let v = Value(5);
    let mut shared = Shared { val: &v };
    let mut b = B::new(&mut shared);
    b.make_a();
}

/*
error[E0621]: explicit lifetime required in the type of `shared`
  --> /Users/yossan/testcodes/rust/garbage/reference_reference.rs:27:21
   |
25 |     fn new(shared: &'a mut Shared) -> Self {
   |                    -------------- help: add explicit lifetime `'a` to the type of `shared`: `&'a mut Shared<'a>`
26 |         B {
27 |             shared: shared,
   |                     ^^^^^^ lifetime `'a` required

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
  --> /Users/yossan/testcodes/rust/garbage/reference_reference.rs:32:17
   |
32 |         let a = A::new(self.shared);
   |                 ^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 31:5...
  --> /Users/yossan/testcodes/rust/garbage/reference_reference.rs:31:5
   |
31 |     fn make_a(&mut self)  -> A {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...so that the expression is assignable
  --> /Users/yossan/testcodes/rust/garbage/reference_reference.rs:33:9
   |
33 |         a
   |         ^
   = note: expected `A<'_>`
              found `A<'_>`
note: but, the lifetime must be valid for the lifetime `'a` as defined on the impl at 24:6...
  --> /Users/yossan/testcodes/rust/garbage/reference_reference.rs:24:6
   |
24 | impl<'a> B<'a> {
   |      ^^
note: ...so that the expression is assignable
  --> /Users/yossan/testcodes/rust/garbage/reference_reference.rs:32:24
   |
32 |         let a = A::new(self.shared);
   |                        ^^^^^^^^^^^
   = note: expected `&mut Shared<'_>`
              found `&mut Shared<'a>`

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0495, E0621.
For more information about an error, try `rustc --explain E0495`.
*/