use std::fmt::{self,Display,Formatter,Write};
use std::string::ToString;

trait Format {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result;
}

impl<'a> Display for Format + 'a {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        Format::fmt(self, f)
    }
}

impl<'a, T: Format> Format for &'a T {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        Ok(())
    }
}

struct Foo<T>(pub Option<T>);

impl<T: Format> Format for Foo<T> {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        Ok(())
    }
}

struct Bar { bar: usize }

impl Format for Bar {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        f.write_str("bar")
    }
}

fn main() {
   let to_string = <Format as ToString>::to_string;
   let i = Bar { bar: 1 };
   let foo = Foo(Some(&i));
   assert_eq!("bar", to_string(&foo));
}