fn main() {
    let words = "Sometimes think, the greatest sorrow than older";
    let foo = Foo::new(words);
    let first = foo.split_first_a();
    println!("{}", first);

    let first = Foo::new(words).split_first_b();
    println!("{}", first);

    println!("{}", Foo::new(words).split_first_a());
}

struct Foo<'a> {
    part: &'a str,
}

impl<'a> Foo<'a> {
    fn split_first_a(&'a self) -> &'a str {
        self.part.split(',').next().expect("Could not find a ','")
    }

    fn split_first_b(&self) -> &'a str {
        self.part.split(',').next().expect("Could not find a ','")
    }

    fn new(s: &'a str) -> Self {
        Foo { part: s }
    }
}