Fn وFnMut وFnOnce

سمات Closure

fn main() {
    let x = 5;
    let show = || println!("x is {}", x); // implements Fn
    show();
    show();
}

Fn: استعارة غير قابلة للتغيير

fn main() {
    let greeting = String::from("Hi");
    let say = || println!("{}", greeting);
    say();
    say();
}

FnMut: استعارة قابلة للتغيير

fn main() {
    let mut count = 0;
    let mut increment = || {
        count += 1;
        println!("count {}", count);
    };
    increment();
    increment();
}

FnOnce: تتولى الملكية

fn main() {
    let name = String::from("Ada");
    let consume = move || {
        let owned = name;
        println!("consumed {}", owned);
    };
    consume();
}

تسلسل السمات الهرمي

fn main() {
    let value = 42;
    let read = || value; // Fn, so also FnMut and FnOnce
    println!("{}", read());
}

تمرير Fn إلى الدوال

fn apply<F: Fn(i32) -> i32>(f: F, x: i32) -> i32 {
    f(x)
}

fn main() {
    let double = |n| n * 2;
    println!("{}", apply(double, 9));
}

قبول FnMut

fn call_twice<F: FnMut()>(mut f: F) {
    f();
    f();
}

fn main() {
    let mut total = 0;
    call_twice(|| total += 1);
    // note: total is borrowed during the call
}

قبول FnOnce

fn run_once<F: FnOnce() -> String>(f: F) {
    let result = f();
    println!("{}", result);
}

fn main() {
    let s = String::from("done");
    run_once(move || s);
}

الكلمة المفتاحية move

fn main() {
    let data = vec![1, 2, 3];
    let printer = move || println!("{:?}", data);
    printer();
}

كيف تختار Rust السمة

fn main() {
    let mut log = Vec::new();
    let mut record = |x: i32| log.push(x); // FnMut
    record(1);
    record(2);
    println!("{:?}", log);
}

اختيار القيد المناسب

fn each<F: Fn(i32)>(items: &[i32], f: F) {
    for &i in items {
        f(i);
    }
}

fn main() {
    each(&[1, 2, 3], |n| println!("got {}", n));
}

تحقق سريع

مراجعة

fn main() {
    let base = 5;
    let adder = move |x: i32| x + base; // Fn, captures base by move
    println!("{}", adder(10));
}