Rust by Example

13.4.4 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`.
struct Borrowed<'a>(&'a i32);

// Similarly, both references here must outlive this structure.
struct NamedBorrowed<'a> {
    x: &'a i32,
    y: &'a i32,

// An enum which is either an `i32` or a reference to one.
enum Either<'a> {
    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: