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

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!
...

Hint: 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 sleep 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