Code shared from the Rust Playground

playground.rs

struct Foo<'a> {
    tokens:Vec<i32>,
    current_tok:Option<&'a i32>,
}

impl<'a> Foo<'a> {
    fn new(tokens:Vec<i32>) -> Foo<'a> {
        Foo {
            tokens,
            current_tok: None,
        }
    }
}

fn main() {

    let mut foo = Foo::new(vec![1,2,5]);
    foo.current_tok = foo.tokens.first();

    match foo.tokens.first() {
        Some(x) => println!("{}",x),
        _ => {},
    }

}