#![feature(try_from)]

use std::convert::TryInto;

struct Foo {
    s: String,
}

impl Foo {
    fn to_bar<'foo>(&'foo self) -> Option<Bar<'foo>> {
        Some(Bar { s: &self.s[1..] })
    }
}


impl<'foo> TryInto<Baz<'foo>> for &'foo Foo {
    type Error = ();

    fn try_into(self) -> Result<Baz<'foo>, ()> {
       if let Some(bar) = self.to_bar() {
            (&bar).try_into()
       } else {
           Err(())
       }
    }
}


struct Bar<'foo> {
    s: &'foo str,
}

impl<'a, 'foo> TryInto<Baz<'foo>> for &'a Bar<'foo> {
    type Error = ();

    fn try_into(self) -> Result<Baz<'foo>, ()> {
        if self.s.ends_with("!") {
            Ok(Baz { s: &self.s[1..] })
        } else {
            Err(())
        }

    }
}

#[derive(Debug)]
struct Baz<'foo> {
    s: &'foo str,
}

fn main() {
    let f = Foo { s: "Foo!".into() };
    let b: Result<Baz, ()> = (&f).try_into();
    println!("{:?}", b);
}