Keyword move

Capture a closure’s environment by value.

move converts any variables captured by reference or mutable reference to variables captured by value.

let data = vec![1, 2, 3];
let closure = move || println!("captured {data:?} by value");

// data is no longer available, it is owned by the closure

Note: move closures may still implement Fn or FnMut, even though they capture variables by move. This is because the traits implemented by a closure type are determined by what the closure does with captured values, not how it captures them:

fn create_fn() -> impl Fn() {
    let text = "Fn".to_owned();
    move || println!("This is a: {text}")
}

let fn_plain = create_fn();
fn_plain();

move is often used when threads are involved.

let data = vec![1, 2, 3];

std::thread::spawn(move || {
    println!("captured {data:?} by value")
}).join().unwrap();

// data was moved to the spawned thread, so we cannot use it here

move is also valid before an async block.

let capture = "hello".to_owned();
let block = async move {
    println!("rust says {capture} from async block");
};

For more information on the move keyword, see the closures section of the Rust book or the threads section.