use std::marker::PhantomData;
use std::ops::Index;

pub trait Context: Clone {
    type Container: ?Sized;
    fn foobar_1( container: &Self::Container ) -> &str;
    fn foobar_2( container: &Self::Container ) -> &str;
    fn foobar_3( container: &Self::Container ) -> &str;
}

#[derive(Clone)]
struct Foobar<'a> {
    phantom: PhantomData<&'a ()>
}

impl<'a> Context for Foobar<'a> {
    type Container = [&'a str];

    fn foobar_1<'r>( container: &'r [&'a str] ) -> &'r str {
        // This compiles fine.
        container[0]
    }

    fn foobar_2<'r>( container: &'r Self::Container ) -> &'r str {
        // This also compiles fine.
        container.index( 0 )
    }

    fn foobar_3<'r>( container: &'r Self::Container ) -> &'r str {
        // error: `*container[..]` does not live long enough
        container[0]
    }
}

fn main() {}