Generalizing over pointer mutability

Question

My use case is a bit more complex than this, but I'm trying to simplify the issue with this abstract example.

Say I have a structure:

struct Foo {
    bar: u32,
    baz: u32,
    ....
}

How can I write a get_bar function which can generalize over the mutability of the self parameter?

Pseudocode:

struct Foo {
    bar: u32,
    baz: u32,
    ....
}

If called with a mutable pointer, it would return a mutble pointer to the inner field, if called with an immutable, it would return an immutable.

My goal is to avoid having to define a nonmut and a mut version of each function, by copy pasting code basically:

impl Foo {
    fn get_bar(&self) -> &u32 { &self.bar }
    fn get_bar_mut(&mut self) -> &mut u32 { &mut self.bar }
}

If the body of the function is more complex than this (my case is a recursive function), it gets pretty nasty, and there is a lot of code that is being copy&pasted, something that should be avoided.