Curriculum Ownership & borrowing Lifetime intuition exercise 1 · mcq-explain

Lifetime intuition

The program below fails: r outlives s. Pick the fix that makes r a valid reference at the println.

Replace r = &s; with r = &s.clone(); — cloning the borrow extends its lifetime.

Move let s = String::from("hi"); UP to the outer scope, above let r;. The reference can only be valid as long as the value it points to is alive.

Annotate the binding: let r: &'static String; — 'static overrides the inner scope's drop.

Leave the layout alone — under non-lexical lifetimes the borrow is automatically extended to cover the println.

About this theme

Lifetimes are not a separate runtime feature; they describe how long references are valid. This theme avoids advanced annotation syntax at first and focuses on why Rust rejects dangling references. Planned exercises: 1. choose the value that lives long enough. 2. recognise a dangling reference. 3. choose owned return instead of borrowed return. 4. fill a scope change that extends an owner. 5. fill a returned String. 6. write a function that returns one of two borrowed inputs with an explicit lifetime. 7. write code that avoids returning a local reference. 8. translate a TS closure over local data. 9. fix a lifetime error by changing ownership rather than adding random annotations.