Understanding Rust Error E0267

Introduction to Rust Error E0267

Rust Error E0267 occurs when a loop keyword (break or continue) is used inside a closure but outside any loop. In this article, we'll discuss the error in detail, provide examples of erroneous code, and give the correct code to help you understand and avoid this error in your Rust code.

Error E0267: An Example

Consider the following Rust code:

fn main() {
  let w = || { break; }; // error: `break` inside of a closure
}

This code will produce the Rust Error E0267 because the break keyword is used inside the closure but outside any loop.

Using break and continue within a Closure

The break and continue keywords can be used within closures, as long as they are also contained within a loop. For example:

fn main() {
  let w = || {
    for _ in 0..10 {
      break;
    }
  };

  w();
}

In this example, the break keyword is used within a closure and inside a loop, so it will not trigger Rust Error E0267.

Using a Return Statement instead of Break

To halt the execution of a closure, you can use a return statement instead of the break keyword. This is particularly useful if you want to exit the closure without necessarily being within a loop. For example:

fn main() {
  let w = || {
    if true {
      return;
    }
    println!("This will not be printed");
  };

  w();
}

This code will halt the execution of the closure when the return statement is executed, without triggering Rust Error E0267.

Conclusion

In summary, Rust Error E0267 occurs when a loop keyword (break or continue) is used inside a closure but outside any loop. To avoid this error, ensure that the break or continue keywords are used within loops in your closures. Alternatively, use a return statement to halt the execution of a closure when appropriate.