error[E0502]: cannot borrow `*self` as mutable because it is also borrowed as immutable
  --> src/lib.rs:20:17
   |
19 |         let a = self.get_a();
   |                 ---- immutable borrow occurs here
20 |         let b = self.get_mut_b();
   |                 ^^^^^^^^^^^^^^^^ mutable borrow occurs here
21 |         println!("{a:?} {b:?}");
   |                    - immutable borrow later used here

error[E0502]: cannot borrow `self.b` as mutable because it is also borrowed as immutable
  --> src/lib.rs:29:9
   |
29 |         self.b.bar(self.get_a());
   |         ^^^^^^^---^----^^^^^^^^^
   |         |      |   |
   |         |      |   immutable borrow occurs here
   |         |      immutable borrow later used by call
   |         mutable borrow occurs here

error[E0502]: cannot borrow `*self` as mutable because it is also borrowed as immutable
  --> src/lib.rs:35:9
   |
35 |         self.bar(self.get_a());
   |         ^^^^^---^----^^^^^^^^^
   |         |    |   |
   |         |    |   immutable borrow occurs here
   |         |    immutable borrow later used by call
   |         mutable borrow occurs here

error[E0502]: cannot borrow `*self` as mutable because it is also borrowed as immutable
  --> src/lib.rs:37:9
   |
37 |         self.bar(&self.a);
   |         ^^^^^---^-------^
   |         |    |   |
   |         |    |   immutable borrow occurs here
   |         |    immutable borrow later used by call
   |         mutable borrow occurs here