Code shared from the Rust Playground

playground.rs

#[derive(Debug)]
enum Bar { 
    A,
    B
}

impl Bar {
    fn as_ref(&self) -> Bar {
        match self {
            Bar::A => Bar::A,
            Bar::B => Bar::B
        }
    }
}

#[derive(Debug)]
enum Message<T> {
    Quit,
    Move { x: i32, y: i32 },
    WriteString(T),
    ChangeColor(i32, i32, i32)
}

impl Message<String> {
    fn as_ref(&self) -> Message<&String> {
        match self {
            Message::Quit => Message::Quit,
            Message::Move { x: x, y: y } => Message::Move { x: *x, y: *y },
            Message::WriteString(ref string) => Message::WriteString(string),
            Message::ChangeColor(r, g, b) => Message::ChangeColor(*r, *g, *b)
        }
    }
}

impl<'a> Message<&'a String> {
    fn as_ref(&self) -> Self {
        match self {
            Message::Quit => Message::Quit,
            Message::Move { x: x, y: y } => Message::Move { x: *x, y: *y },
            Message::WriteString(string) => Message::WriteString(string),
            Message::ChangeColor(r, g, b) => Message::ChangeColor(*r, *g, *b)
        }
    }
}

fn main() {
    let b = Bar::B {};
    let b = b.as_ref();
    println!("{:?}", b);
    
    let s = "s".to_string();
    let m = &Message::WriteString(s);
    println!("{:?}", m.as_ref())
}