gistfile1.rs

trait CoerceFrom<T> {
    fn coerce_from(T) -> Self;
}

trait Coerce  {
    fn coerce<T>(self) -> T where T: CoerceFrom<Self>;
}

impl<T> Coerce for T {
    fn coerce<U: CoerceFrom<T>>(self) -> U {
        CoerceFrom::coerce_from(self)
    }
}

impl<'a> CoerceFrom<&'a String> for &'a str {
    fn coerce_from(s: &'a String) -> &'a str {
        s.as_slice()
    }
}

impl<'a> CoerceFrom<&'a String> for &'a [u8] {
    fn coerce_from(s: &'a String) -> &'a [u8] {
        s.as_bytes()
    }
}

fn main() {
    let s = format!("hello");
    // let b: &[u8] = s.coerce();  // fails
    let b: &[u8] = (&s).coerce();
}