How do I idiomatically convert a bool to an Option or Result in Rust?

As of Rust 1.50 you can use bool::then:

assert_eq!(false.then(|| val), None);
assert_eq!(true.then(|| val), Some(val));

You can convert it to a Result by chaining Option::ok_or:

assert_eq!(false.then(|| val).ok_or(err), Err(err));
assert_eq!(true.then(|| val).ok_or(err), Ok(val));

As of Rust 1.62, you can use bool::then_some and pass a value directly instead of creating a closure:

assert_eq!(false.then_some(val), None);
assert_eq!(true.then_some(val), Some(val));

Alternatively, you can use Option::filter:

assert_eq!(Some(obj).filter(|_| false), None);
assert_eq!(Some(obj).filter(|_| true).ok_or(err), Ok(obj));

bool.then_some() does this:

let my_bool = true;
let my_option = my_bool.then_some(MyObject{});
let my_result = my_bool.then_some(MyObject{}).ok_or(MyError{});

At the time of writing, this is still part of the experimental bool_to_option feature.

Update: As of Rust 1.62, this feature has been stabilized.

Related