Curriculum Collections & iteration Closures exercise 3 · mcq-explain

Closures

When should you write move || in front of a Rust closure?

TypeScript reference

Only when the closure mutates captured state; without move, mutation is forbidden.

Always — move makes closures safer by avoiding hidden references.

When the closure returns a value larger than 8 bytes, to avoid copying on return.

Add move when the closure must OUTLIVE the local borrows it would otherwise take — typically when handing the closure to another thread or storing it in a struct. move forces capture by VALUE; without it the compiler picks the lightest mode (borrow, then mut-borrow, then move).

About this theme

Rust closures look like compact TypeScript arrow functions, but they capture by borrow, mutable borrow, or move depending on use. Planned exercises: 1. choose closure syntax. 2. recognise inferred parameter types. 3. choose move only when ownership must transfer. 4. fill a predicate closure. 5. fill a mapping closure. 6. write a closure used with sort_by_key. 7. write a closure that captures a threshold. 8. translate TS arrow functions in array methods. 9. fix a closure capture that conflicts with a later borrow.