use std::vec::Vec;
use std::option::Option;

trait MyTrait {
    fn bar(&self, vec: &Vec<u32>) -> Option<&u32>;
}

struct Foo;

impl MyTrait for Foo {
    fn bar<'a>(&self, vec: &'a Vec<u32>) -> Option<&'a u32> {
        vec.get(0)
    }
}

fn main() {}