trait Foo {
    fn fn1(&self) -> i32;
}

struct FooImpl;

impl Foo for FooImpl {
    fn fn1(&self) -> i32 { 1 }
}

trait FooExt : Foo {
    fn fn_ext(&self) -> i32 {
        self.fn1() + 1
    }
}

impl<T: Foo> FooExt for T {}

impl<'a> Foo for &'a Foo {
    fn fn1(&self) -> i32 {
        (*self).fn1()
    }
}

fn func(f: &Foo) {
    println!("func fn1: {}", f.fn1());
    println!("func fn_ext: {}", f.fn_ext());
}

fn main() {
    let f = FooImpl;
    println!("fn1: {}", f.fn1());
    println!("fn_ext: {}", f.fn_ext());
    func(&f);
}