Loops

Loops are a fundamental building block common to many programming languages. This is no exception in Rune. Loops allow you to execute a block of code until a specific condition is reached, which can be a powerful tool for accomplishing programming tasks.

break Keyword

Every loop documented in this section can be terminated early using the break keyword.

When Rune encounters a break, it will immediately jump out of the loop it is currently in and continue running right after it.

pub fn main() {
    let value = 0;

    while value < 100 {
        if value >= 50 {
            break;
        }

        value = value + 1;
    }

    println!("The value is {}", value); // => The value is 50
}

$> cargo run --bin rune -- run scripts/book/loops/while_loop.rn
The value is 50
== () (501.1µs)

loop Expressions

The loop keyword builds the most fundamental form of loop in Rune. One that repeats unconditionally forever, until it is exited using another control flow operator like a break or a return.

use time::Duration;

pub async fn main() {
    loop {
        println("Hello forever!");
        time::sleep(Duration::from_secs(1)).await;
    }
}

$> cargo run --bin rune -- run scripts/book/loops/loop_forever.rn
Hello forever!
Hello forever!
Hello forever!
...

If you want this one to end, you're gonna have to kill it with CTRL+C.

We're also using an asynchronous function called delay_for above to avoid spamming our terminals too much. Well talk more about these in a later section.

When broken out of, loops produce the value provided as an argument to the break keyword. By default, this is simply a unit ().

pub fn main() {
    let counter = 0;

    let total = loop {
        counter = counter + 1;

        if counter > 10 {
            break counter;
        }
    };

    println!("The final count is: {}", total);
}

$> cargo run --bin rune -- run scripts/book/loops/loop_break.rn
The final count is: 11
== () (281.5µs)