# Structs

Annotation of lifetimes in structures are also similar to functions:

    // A type `Borrowed` which houses a reference to an
    // `i32`. The reference to `i32` must outlive `Borrowed`.
    #[derive(Debug)]
    struct Borrowed<'a>(&'a i32);

    // Similarly, both references here must outlive this structure.
    #[derive(Debug)]
    struct NamedBorrowed<'a> {
        x: &'a i32,
        y: &'a i32,
    }

    // An enum which is either an `i32` or a reference to one.
    #[derive(Debug)]
    enum Either<'a> {
        Num(i32),
        Ref(&'a i32),
    }

    fn main() {
        let x = 18;
        let y = 15;

        let single = Borrowed(&x);
        let double = NamedBorrowed { x: &x, y: &y };
        let reference = Either::Ref(&x);
        let number    = Either::Num(y);

        println!("x is borrowed in {:?}", single);
        println!("x and y are borrowed in {:?}", double);
        println!("x is borrowed in {:?}", reference);
        println!("y is *not* borrowed in {:?}", number);
    }

### See also:

`structs`