E0502: Break with value

Explanation

Rue loops currently produce only () when exited by break. A break therefore cannot carry a value operand: break expression is rejected even when the surrounding loop appears in a value position.

Likely cause

Code used break value expecting that value to become the result of a loop. Store the value in a mutable binding before a valueless break, or restructure the code so the desired value is produced after the loop.

Examples

Break with a value operand

fn main() -> i32 {
    loop {
        break 42;
    }
}

Store the value before breaking

fn main() -> i32 {
    let mut answer = 0;
    loop {
        answer = 42;
        break;
    }
    answer
}

References

• Loops exited by break produce unit

• Break has no value operand